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 $236.51   13.864%   $269.2997   $269.30   $269.30   $269.30  
  Purchase #2 $77.31   4.844%   $81.0549   $81.05   $81.05   $81.10  
  Purchase #3 $157.78   8.648%   $171.4248   $171.42   $171.40   $171.40  
  Purchase #4 $124.94   10.844%   $138.4885   $138.49   $138.50   $138.50  
  Purchase #5 $221.77   12.777%   $250.1056   $250.11   $250.10   $250.10  
  Purchase #6 $60.33   13.603%   $68.5367   $68.54   $68.55   $68.50  
  Purchase #7 $47.97   9.743%   $52.6437   $52.64   $52.65   $52.60  
  7 purchase totals = $926.61       $1,031.5539   $1,031.55   $1,031.55   $1,031.50