Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $203.82   11.453%   $227.1635   $227.16   $227.15   $227.20  
  Purchase #2 $208.56   12.676%   $234.9971   $235.00   $235.00   $235.00  
  Purchase #3 $174.73   5.535%   $184.4013   $184.40   $184.40   $184.40  
  Purchase #4 $246.78   7.145%   $264.4124   $264.41   $264.40   $264.40  
  Purchase #5 $146.89   13.279%   $166.3955   $166.40   $166.40   $166.40  
  Purchase #6 $171.56   7.653%   $184.6895   $184.69   $184.70   $184.70  
  Purchase #7 $153.75   7.577%   $165.3996   $165.40   $165.40   $165.40  
  7 purchase totals = $1,306.09       $1,427.4589   $1,427.46   $1,427.45   $1,427.50