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 $89.73   4.464%   $93.7355   $93.74   $93.75   $93.70  
  Purchase #2 $223.88   10.163%   $246.6329   $246.63   $246.65   $246.60  
  Purchase #3 $207.56   4.338%   $216.564   $216.56   $216.55   $216.60  
  Purchase #4 $163.53   3.775%   $169.7033   $169.70   $169.70   $169.70  
  Purchase #5 $142.70   8.652%   $155.0464   $155.05   $155.05   $155.00  
  Purchase #6 $245.82   9.446%   $269.0402   $269.04   $269.05   $269.00  
  Purchase #7 $191.93   12.592%   $216.0978   $216.10   $216.10   $216.10  
  7 purchase totals = $1,265.15       $1,366.8201   $1,366.82   $1,366.85   $1,366.70