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 $84.29   12.779%   $95.0614   $95.06   $95.05   $95.10  
  Purchase #2 $112.35   6.433%   $119.5775   $119.58   $119.60   $119.60  
  Purchase #3 $84.88   7.665%   $91.3861   $91.39   $91.40   $91.40  
  Purchase #4 $234.34   12.483%   $263.5927   $263.59   $263.60   $263.60  
  Purchase #5 $97.75   6.183%   $103.7939   $103.79   $103.80   $103.80  
  Purchase #6 $36.44   7.165%   $39.0509   $39.05   $39.05   $39.10  
  Purchase #7 $112.46   9.645%   $123.3068   $123.31   $123.30   $123.30  
  7 purchase totals = $762.51       $835.7693   $835.77   $835.80   $835.90