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 $54.69   8.495%   $59.3359   $59.34   $59.35   $59.30  
  Purchase #2 $80.59   9.654%   $88.3702   $88.37   $88.35   $88.40  
  Purchase #3 $160.34   8.381%   $173.7781   $173.78   $173.80   $173.80  
  Purchase #4 $59.61   11.395%   $66.4026   $66.40   $66.40   $66.40  
  Purchase #5 $87.50   10.823%   $96.9701   $96.97   $96.95   $97.00  
  Purchase #6 $157.38   13.546%   $178.6987   $178.70   $178.70   $178.70  
  Purchase #7 $121.74   11.267%   $135.4564   $135.46   $135.45   $135.50  
  7 purchase totals = $721.85       $799.0120   $799.02   $799.00   $799.10