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 $111.92   6.347%   $119.0236   $119.02   $119.00   $119.00  
  Purchase #2 $186.58   10.645%   $206.4414   $206.44   $206.45   $206.40  
  Purchase #3 $188.55   11.574%   $210.3728   $210.37   $210.35   $210.40  
  Purchase #4 $194.75   8.687%   $211.6679   $211.67   $211.65   $211.70  
  Purchase #5 $94.27   4.612%   $98.6177   $98.62   $98.60   $98.60  
  Purchase #6 $119.39   13.855%   $135.9315   $135.93   $135.95   $135.90  
  Purchase #7 $88.43   4.489%   $92.3996   $92.40   $92.40   $92.40  
  7 purchase totals = $983.89       $1,074.4545   $1,074.45   $1,074.40   $1,074.40