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 $62.64   13.863%   $71.3238   $71.32   $71.30   $71.30  
  Purchase #2 $238.32   12.376%   $267.8145   $267.81   $267.80   $267.80  
  Purchase #3 $64.48   6.796%   $68.8621   $68.86   $68.85   $68.90  
  Purchase #4 $102.66   12.640%   $115.6362   $115.64   $115.65   $115.60  
  Purchase #5 $236.87   13.619%   $269.1293   $269.13   $269.15   $269.10  
  Purchase #6 $95.92   8.792%   $104.3533   $104.35   $104.35   $104.40  
  Purchase #7 $97.66   10.411%   $107.8274   $107.83   $107.85   $107.80  
  7 purchase totals = $898.55       $1,004.9466   $1,004.94   $1,004.95   $1,004.90