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 $58.71   6.308%   $62.4134   $62.41   $62.40   $62.40  
  Purchase #2 $9.41   9.480%   $10.3021   $10.30   $10.30   $10.30  
  Purchase #3 $115.55   7.185%   $123.8523   $123.85   $123.85   $123.90  
  Purchase #4 $29.63   11.595%   $33.0656   $33.07   $33.05   $33.10  
  Purchase #5 $67.70   13.827%   $77.0609   $77.06   $77.05   $77.10  
  Purchase #6 $247.31   5.381%   $260.6178   $260.62   $260.60   $260.60  
  Purchase #7 $247.94   8.425%   $268.8289   $268.83   $268.85   $268.80  
  7 purchase totals = $776.25       $836.1410   $836.14   $836.10   $836.20