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 $40.73   8.771%   $44.3024   $44.30   $44.30   $44.30  
  Purchase #2 $196.93   8.302%   $213.2791   $213.28   $213.30   $213.30  
  Purchase #3 $155.79   9.551%   $170.6695   $170.67   $170.65   $170.70  
  Purchase #4 $195.87   5.650%   $206.9367   $206.94   $206.95   $206.90  
  Purchase #5 $192.90   8.732%   $209.744   $209.74   $209.75   $209.70  
  Purchase #6 $187.77   12.772%   $211.752   $211.75   $211.75   $211.80  
  Purchase #7 $139.34   3.155%   $143.7362   $143.74   $143.75   $143.70  
  7 purchase totals = $1,109.33       $1,200.4199   $1,200.42   $1,200.45   $1,200.40