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 $48.71   13.607%   $55.338   $55.34   $55.35   $55.30  
  Purchase #2 $69.36   8.299%   $75.1162   $75.12   $75.10   $75.10  
  Purchase #3 $229.25   5.122%   $240.9922   $240.99   $241.00   $241.00  
  Purchase #4 $236.55   6.506%   $251.9399   $251.94   $251.95   $251.90  
  Purchase #5 $53.89   5.838%   $57.0361   $57.04   $57.05   $57.00  
  Purchase #6 $237.74   3.572%   $246.2321   $246.23   $246.25   $246.20  
  Purchase #7 $89.79   3.297%   $92.7504   $92.75   $92.75   $92.80  
  7 purchase totals = $965.29       $1,019.4049   $1,019.41   $1,019.45   $1,019.30