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 $62.97   7.273%   $67.5498   $67.55   $67.55   $67.50  
  Purchase #2 $56.62   11.278%   $63.0056   $63.01   $63.00   $63.00  
  Purchase #3 $147.36   3.303%   $152.2273   $152.23   $152.25   $152.20  
  Purchase #4 $153.57   10.571%   $169.8039   $169.80   $169.80   $169.80  
  Purchase #5 $45.66   11.498%   $50.91   $50.91   $50.90   $50.90  
  Purchase #6 $120.43   8.725%   $130.9375   $130.94   $130.95   $130.90  
  Purchase #7 $70.98   6.563%   $75.6384   $75.64   $75.65   $75.60  
  7 purchase totals = $657.59       $710.0725   $710.08   $710.10   $709.90