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 $122.86   5.589%   $129.7266   $129.73   $129.75   $129.70  
  Purchase #2 $143.82   9.870%   $158.015   $158.02   $158.00   $158.00  
  Purchase #3 $15.34   6.791%   $16.3817   $16.38   $16.40   $16.40  
  Purchase #4 $128.85   12.792%   $145.3325   $145.33   $145.35   $145.30  
  Purchase #5 $150.38   6.614%   $160.3261   $160.33   $160.35   $160.30  
  Purchase #6 $154.32   5.664%   $163.0607   $163.06   $163.05   $163.10  
  Purchase #7 $96.71   11.704%   $108.0289   $108.03   $108.05   $108.00  
  7 purchase totals = $812.28       $880.8715   $880.88   $880.95   $880.80