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 $56.42   8.488%   $61.2089   $61.21   $61.20   $61.20  
  Purchase #2 $119.42   5.217%   $125.6501   $125.65   $125.65   $125.70  
  Purchase #3 $83.37   10.358%   $92.0055   $92.01   $92.00   $92.00  
  Purchase #4 $128.66   10.450%   $142.105   $142.11   $142.10   $142.10  
  Purchase #5 $235.61   11.447%   $262.5803   $262.58   $262.60   $262.60  
  Purchase #6 $155.76   5.424%   $164.2084   $164.21   $164.20   $164.20  
  Purchase #7 $83.58   8.753%   $90.8958   $90.90   $90.90   $90.90  
  7 purchase totals = $862.82       $938.6540   $938.67   $938.65   $938.70