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 $59.84   11.402%   $66.663   $66.66   $66.65   $66.70  
  Purchase #2 $199.39   6.608%   $212.5657   $212.57   $212.55   $212.60  
  Purchase #3 $36.72   13.450%   $41.6588   $41.66   $41.65   $41.70  
  Purchase #4 $67.29   4.245%   $70.1465   $70.15   $70.15   $70.10  
  Purchase #5 $250.98   4.749%   $262.899   $262.90   $262.90   $262.90  
  Purchase #6 $42.75   9.362%   $46.7523   $46.75   $46.75   $46.80  
  Purchase #7 $56.82   6.345%   $60.4252   $60.43   $60.45   $60.40  
  7 purchase totals = $713.79       $761.1105   $761.12   $761.10   $761.20