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 $196.39   11.818%   $219.5994   $219.60   $219.60   $219.60  
  Purchase #2 $174.39   4.364%   $182.0004   $182.00   $182.00   $182.00  
  Purchase #3 $222.84   4.325%   $232.4778   $232.48   $232.50   $232.50  
  Purchase #4 $72.35   5.519%   $76.343   $76.34   $76.35   $76.30  
  Purchase #5 $215.73   3.204%   $222.642   $222.64   $222.65   $222.60  
  Purchase #6 $225.36   4.477%   $235.4494   $235.45   $235.45   $235.40  
  Purchase #7 $158.36   3.607%   $164.072   $164.07   $164.05   $164.10  
  7 purchase totals = $1,265.42       $1,332.5840   $1,332.58   $1,332.60   $1,332.50