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 $53.72   12.756%   $60.5725   $60.57   $60.55   $60.60  
  Purchase #2 $62.43   4.142%   $65.0159   $65.02   $65.00   $65.00  
  Purchase #3 $104.36   4.583%   $109.1428   $109.14   $109.15   $109.10  
  Purchase #4 $195.47   3.378%   $202.073   $202.07   $202.05   $202.10  
  Purchase #5 $77.79   6.692%   $82.9957   $83.00   $83.00   $83.00  
  Purchase #6 $200.93   3.359%   $207.6792   $207.68   $207.70   $207.70  
  Purchase #7 $32.73   13.769%   $37.2366   $37.24   $37.25   $37.20  
  7 purchase totals = $727.43       $764.7157   $764.72   $764.70   $764.70