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 $201.80   10.681%   $223.3543   $223.35   $223.35   $223.40  
  Purchase #2 $121.92   9.870%   $133.9535   $133.95   $133.95   $134.00  
  Purchase #3 $23.85   3.292%   $24.6351   $24.64   $24.65   $24.60  
  Purchase #4 $135.68   13.380%   $153.834   $153.83   $153.85   $153.80  
  Purchase #5 $87.62   12.841%   $98.8713   $98.87   $98.85   $98.90  
  Purchase #6 $203.62   8.232%   $220.382   $220.38   $220.40   $220.40  
  Purchase #7 $80.45   13.639%   $91.4226   $91.42   $91.40   $91.40  
  7 purchase totals = $854.94       $946.4528   $946.44   $946.45   $946.50