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 $114.61   4.276%   $119.5107   $119.51   $119.50   $119.50  
  Purchase #2 $56.75   13.354%   $64.3284   $64.33   $64.35   $64.30  
  Purchase #3 $148.32   3.661%   $153.75   $153.75   $153.75   $153.80  
  Purchase #4 $143.25   12.693%   $161.4327   $161.43   $161.45   $161.40  
  Purchase #5 $213.85   8.853%   $232.7821   $232.78   $232.80   $232.80  
  Purchase #6 $143.46   9.463%   $157.0356   $157.04   $157.05   $157.00  
  Purchase #7 $163.45   3.401%   $169.0089   $169.01   $169.00   $169.00  
  7 purchase totals = $983.69       $1,057.8484   $1,057.85   $1,057.90   $1,057.80