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 $119.33   4.142%   $124.2726   $124.27   $124.25   $124.30  
  Purchase #2 $57.44   9.280%   $62.7704   $62.77   $62.75   $62.80  
  Purchase #3 $225.66   4.403%   $235.5958   $235.60   $235.60   $235.60  
  Purchase #4 $224.71   8.517%   $243.8486   $243.85   $243.85   $243.80  
  Purchase #5 $21.66   13.809%   $24.651   $24.65   $24.65   $24.70  
  Purchase #6 $200.46   3.542%   $207.5603   $207.56   $207.55   $207.60  
  Purchase #7 $31.72   10.862%   $35.1654   $35.17   $35.15   $35.20  
  7 purchase totals = $880.98       $933.8641   $933.87   $933.80   $934.00