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 $84.34   10.611%   $93.2893   $93.29   $93.30   $93.30  
  Purchase #2 $235.30   7.148%   $252.1192   $252.12   $252.10   $252.10  
  Purchase #3 $68.76   13.397%   $77.9718   $77.97   $77.95   $78.00  
  Purchase #4 $44.60   13.382%   $50.5684   $50.57   $50.55   $50.60  
  Purchase #5 $215.77   12.299%   $242.3076   $242.31   $242.30   $242.30  
  Purchase #6 $214.55   7.140%   $229.8689   $229.87   $229.85   $229.90  
  Purchase #7 $69.28   12.677%   $78.0626   $78.06   $78.05   $78.10  
  7 purchase totals = $932.60       $1,024.1878   $1,024.19   $1,024.10   $1,024.30