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 $206.84   9.426%   $226.3367   $226.34   $226.35   $226.30  
  Purchase #2 $47.87   8.586%   $51.9801   $51.98   $52.00   $52.00  
  Purchase #3 $25.43   5.800%   $26.9049   $26.90   $26.90   $26.90  
  Purchase #4 $91.66   5.594%   $96.7875   $96.79   $96.80   $96.80  
  Purchase #5 $101.35   10.804%   $112.2999   $112.30   $112.30   $112.30  
  Purchase #6 $89.89   8.218%   $97.2772   $97.28   $97.30   $97.30  
  Purchase #7 $167.58   8.174%   $181.278   $181.28   $181.30   $181.30  
  7 purchase totals = $730.62       $792.8643   $792.87   $792.95   $792.90