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 $14.66   12.281%   $16.4604   $16.46   $16.45   $16.50  
  Purchase #2 $200.79   10.210%   $221.2907   $221.29   $221.30   $221.30  
  Purchase #3 $164.42   9.359%   $179.8081   $179.81   $179.80   $179.80  
  Purchase #4 $197.43   13.192%   $223.475   $223.48   $223.50   $223.50  
  Purchase #5 $57.49   6.182%   $61.044   $61.04   $61.05   $61.00  
  Purchase #6 $77.36   7.388%   $83.0754   $83.08   $83.10   $83.10  
  Purchase #7 $102.43   10.146%   $112.8225   $112.82   $112.80   $112.80  
  7 purchase totals = $814.58       $897.9761   $897.98   $898.00   $898.00