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 $55.28   9.822%   $60.7096   $60.71   $60.70   $60.70  
  Purchase #2 $93.32   13.424%   $105.8473   $105.85   $105.85   $105.80  
  Purchase #3 $139.71   8.710%   $151.8787   $151.88   $151.90   $151.90  
  Purchase #4 $86.86   12.583%   $97.7896   $97.79   $97.80   $97.80  
  Purchase #5 $20.98   13.859%   $23.8876   $23.89   $23.90   $23.90  
  Purchase #6 $241.82   5.245%   $254.5035   $254.50   $254.50   $254.50  
  Purchase #7 $93.97   13.490%   $106.6466   $106.65   $106.65   $106.60  
  7 purchase totals = $731.94       $801.2629   $801.27   $801.30   $801.20