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 $173.97   10.751%   $192.6735   $192.67   $192.65   $192.70  
  Purchase #2 $241.30   10.399%   $266.3928   $266.39   $266.40   $266.40  
  Purchase #3 $19.68   4.802%   $20.625   $20.63   $20.65   $20.60  
  Purchase #4 $87.95   11.258%   $97.8514   $97.85   $97.85   $97.90  
  Purchase #5 $12.53   11.541%   $13.9761   $13.98   $14.00   $14.00  
  Purchase #6 $217.30   10.416%   $239.934   $239.93   $239.95   $239.90  
  Purchase #7 $24.43   6.189%   $25.942   $25.94   $25.95   $25.90  
  7 purchase totals = $777.16       $857.3948   $857.39   $857.45   $857.40