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 $67.38   8.756%   $73.2798   $73.28   $73.30   $73.30  
  Purchase #2 $190.37   11.773%   $212.7823   $212.78   $212.80   $212.80  
  Purchase #3 $147.42   7.441%   $158.3895   $158.39   $158.40   $158.40  
  Purchase #4 $50.77   11.317%   $56.5156   $56.52   $56.50   $56.50  
  Purchase #5 $130.28   9.165%   $142.2202   $142.22   $142.20   $142.20  
  Purchase #6 $216.92   12.498%   $244.0307   $244.03   $244.05   $244.00  
  Purchase #7 $145.91   6.396%   $155.2424   $155.24   $155.25   $155.20  
  7 purchase totals = $949.05       $1,042.4605   $1,042.46   $1,042.50   $1,042.40