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 $57.47   8.689%   $62.4636   $62.46   $62.45   $62.50  
  Purchase #2 $92.59   12.716%   $104.3637   $104.36   $104.35   $104.40  
  Purchase #3 $167.70   3.315%   $173.2593   $173.26   $173.25   $173.30  
  Purchase #4 $225.80   7.669%   $243.1166   $243.12   $243.10   $243.10  
  Purchase #5 $109.43   10.580%   $121.0077   $121.01   $121.00   $121.00  
  Purchase #6 $158.78   3.826%   $164.8549   $164.85   $164.85   $164.90  
  Purchase #7 $26.88   7.820%   $28.982   $28.98   $29.00   $29.00  
  7 purchase totals = $838.65       $898.0478   $898.04   $898.00   $898.20