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 $57.45   10.840%   $63.6776   $63.68   $63.70   $63.70  
  Purchase #2 $202.25   8.110%   $218.6525   $218.65   $218.65   $218.70  
  Purchase #3 $218.48   4.559%   $228.4405   $228.44   $228.45   $228.40  
  Purchase #4 $246.82   10.516%   $272.7756   $272.78   $272.80   $272.80  
  Purchase #5 $214.32   13.566%   $243.3947   $243.39   $243.40   $243.40  
  Purchase #6 $97.66   6.530%   $104.0372   $104.04   $104.05   $104.00  
  Purchase #7 $235.98   10.725%   $261.2889   $261.29   $261.30   $261.30  
  7 purchase totals = $1,272.96       $1,392.2670   $1,392.27   $1,392.35   $1,392.30