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 $81.67   13.272%   $92.5092   $92.51   $92.50   $92.50  
  Purchase #2 $209.34   4.745%   $219.2732   $219.27   $219.25   $219.30  
  Purchase #3 $9.38   5.822%   $9.9261   $9.93   $9.95   $9.90  
  Purchase #4 $64.62   12.125%   $72.4552   $72.46   $72.45   $72.50  
  Purchase #5 $117.99   11.584%   $131.658   $131.66   $131.65   $131.70  
  Purchase #6 $231.99   5.216%   $244.0906   $244.09   $244.10   $244.10  
  Purchase #7 $230.31   9.328%   $251.7933   $251.79   $251.80   $251.80  
  7 purchase totals = $945.30       $1,021.7056   $1,021.71   $1,021.70   $1,021.80