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 $200.56   11.157%   $222.9365   $222.94   $222.95   $222.90  
  Purchase #2 $30.44   10.254%   $33.5613   $33.56   $33.55   $33.60  
  Purchase #3 $173.92   6.254%   $184.797   $184.80   $184.80   $184.80  
  Purchase #4 $54.98   13.445%   $62.3721   $62.37   $62.35   $62.40  
  Purchase #5 $86.26   13.437%   $97.8508   $97.85   $97.85   $97.90  
  Purchase #6 $95.96   10.578%   $106.1106   $106.11   $106.10   $106.10  
  Purchase #7 $148.38   3.737%   $153.925   $153.93   $153.95   $153.90  
  7 purchase totals = $790.50       $861.5533   $861.56   $861.55   $861.60