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 $89.57   5.762%   $94.731   $94.73   $94.75   $94.70  
  Purchase #2 $55.67   8.353%   $60.3201   $60.32   $60.30   $60.30  
  Purchase #3 $102.34   5.817%   $108.2931   $108.29   $108.30   $108.30  
  Purchase #4 $20.88   9.861%   $22.939   $22.94   $22.95   $22.90  
  Purchase #5 $243.48   12.291%   $273.4061   $273.41   $273.40   $273.40  
  Purchase #6 $248.77   12.739%   $280.4608   $280.46   $280.45   $280.50  
  Purchase #7 $193.82   10.124%   $213.4423   $213.44   $213.45   $213.40  
  7 purchase totals = $954.53       $1,053.5924   $1,053.59   $1,053.60   $1,053.50