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 $87.30   12.273%   $98.0143   $98.01   $98.00   $98.00  
  Purchase #2 $106.87   9.740%   $117.2791   $117.28   $117.30   $117.30  
  Purchase #3 $115.63   6.368%   $122.9933   $122.99   $123.00   $123.00  
  Purchase #4 $229.38   5.685%   $242.4203   $242.42   $242.40   $242.40  
  Purchase #5 $55.68   11.213%   $61.9234   $61.92   $61.90   $61.90  
  Purchase #6 $235.89   11.261%   $262.4536   $262.45   $262.45   $262.50  
  Purchase #7 $105.54   4.468%   $110.2555   $110.26   $110.25   $110.30  
  7 purchase totals = $936.29       $1,015.3395   $1,015.33   $1,015.30   $1,015.40