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 $93.29   3.692%   $96.7343   $96.73   $96.75   $96.70  
  Purchase #2 $228.65   7.210%   $245.1357   $245.14   $245.15   $245.10  
  Purchase #3 $179.46   11.726%   $200.5035   $200.50   $200.50   $200.50  
  Purchase #4 $50.41   6.759%   $53.8172   $53.82   $53.80   $53.80  
  Purchase #5 $22.61   4.494%   $23.6261   $23.63   $23.65   $23.60  
  Purchase #6 $92.32   13.440%   $104.7278   $104.73   $104.75   $104.70  
  Purchase #7 $28.51   9.641%   $31.2586   $31.26   $31.25   $31.30  
  7 purchase totals = $695.25       $755.8032   $755.81   $755.85   $755.70