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 $73.91   6.183%   $78.4799   $78.48   $78.50   $78.50  
  Purchase #2 $33.27   4.278%   $34.6933   $34.69   $34.70   $34.70  
  Purchase #3 $184.31   8.657%   $200.2657   $200.27   $200.25   $200.30  
  Purchase #4 $78.82   11.325%   $87.7464   $87.75   $87.75   $87.70  
  Purchase #5 $71.69   3.843%   $74.445   $74.45   $74.45   $74.40  
  Purchase #6 $199.60   6.775%   $213.1229   $213.12   $213.10   $213.10  
  Purchase #7 $223.64   8.792%   $243.3024   $243.30   $243.30   $243.30  
  7 purchase totals = $865.24       $932.0556   $932.06   $932.05   $932.00