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 $217.27   4.363%   $226.7495   $226.75   $226.75   $226.70  
  Purchase #2 $185.39   3.326%   $191.5561   $191.56   $191.55   $191.60  
  Purchase #3 $53.96   11.347%   $60.0828   $60.08   $60.10   $60.10  
  Purchase #4 $199.87   10.478%   $220.8124   $220.81   $220.80   $220.80  
  Purchase #5 $162.32   3.162%   $167.4526   $167.45   $167.45   $167.50  
  Purchase #6 $240.65   12.582%   $270.9286   $270.93   $270.95   $270.90  
  Purchase #7 $133.77   5.325%   $140.8933   $140.89   $140.90   $140.90  
  7 purchase totals = $1,193.23       $1,278.4753   $1,278.47   $1,278.50   $1,278.50