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 $129.86   5.731%   $137.3023   $137.30   $137.30   $137.30  
  Purchase #2 $219.30   3.680%   $227.3702   $227.37   $227.35   $227.40  
  Purchase #3 $209.26   3.538%   $216.6636   $216.66   $216.65   $216.70  
  Purchase #4 $62.51   5.142%   $65.7243   $65.72   $65.70   $65.70  
  Purchase #5 $124.37   9.571%   $136.2735   $136.27   $136.25   $136.30  
  Purchase #6 $211.40   10.800%   $234.2312   $234.23   $234.25   $234.20  
  Purchase #7 $126.84   4.511%   $132.5618   $132.56   $132.55   $132.60  
  7 purchase totals = $1,083.54       $1,150.1269   $1,150.11   $1,150.05   $1,150.20