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 $71.52   5.716%   $75.6081   $75.61   $75.60   $75.60  
  Purchase #2 $81.99   11.724%   $91.6025   $91.60   $91.60   $91.60  
  Purchase #3 $204.70   4.191%   $213.279   $213.28   $213.30   $213.30  
  Purchase #4 $174.91   9.258%   $191.1032   $191.10   $191.10   $191.10  
  Purchase #5 $248.93   4.306%   $259.6489   $259.65   $259.65   $259.60  
  Purchase #6 $99.34   5.191%   $104.4967   $104.50   $104.50   $104.50  
  Purchase #7 $54.29   5.223%   $57.1256   $57.13   $57.15   $57.10  
  7 purchase totals = $935.68       $992.8640   $992.87   $992.90   $992.80