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 $185.27   9.578%   $203.0152   $203.02   $203.00   $203.00  
  Purchase #2 $109.51   13.787%   $124.6081   $124.61   $124.60   $124.60  
  Purchase #3 $52.45   11.140%   $58.2929   $58.29   $58.30   $58.30  
  Purchase #4 $143.95   12.726%   $162.2691   $162.27   $162.25   $162.30  
  Purchase #5 $98.41   5.811%   $104.1286   $104.13   $104.15   $104.10  
  Purchase #6 $85.66   11.713%   $95.6934   $95.69   $95.70   $95.70  
  Purchase #7 $12.94   12.535%   $14.562   $14.56   $14.55   $14.60  
  7 purchase totals = $688.19       $762.5693   $762.57   $762.55   $762.60