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 $59.49   4.222%   $62.0017   $62.00   $62.00   $62.00  
  Purchase #2 $224.29   8.807%   $244.0432   $244.04   $244.05   $244.00  
  Purchase #3 $42.59   10.118%   $46.8993   $46.90   $46.90   $46.90  
  Purchase #4 $205.88   4.292%   $214.7164   $214.72   $214.70   $214.70  
  Purchase #5 $21.65   13.480%   $24.5684   $24.57   $24.55   $24.60  
  Purchase #6 $203.82   13.696%   $231.7352   $231.74   $231.75   $231.70  
  Purchase #7 $19.60   11.478%   $21.8497   $21.85   $21.85   $21.80  
  7 purchase totals = $777.32       $845.8139   $845.82   $845.80   $845.70