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 $55.95   9.182%   $61.0873   $61.09   $61.10   $61.10  
  Purchase #2 $65.45   4.430%   $68.3494   $68.35   $68.35   $68.30  
  Purchase #3 $93.36   6.776%   $99.6861   $99.69   $99.70   $99.70  
  Purchase #4 $28.83   10.680%   $31.909   $31.91   $31.90   $31.90  
  Purchase #5 $197.74   5.624%   $208.8609   $208.86   $208.85   $208.90  
  Purchase #6 $52.53   3.546%   $54.3927   $54.39   $54.40   $54.40  
  Purchase #7 $110.72   3.553%   $114.6539   $114.65   $114.65   $114.70  
  7 purchase totals = $604.58       $638.9393   $638.94   $638.95   $639.00