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 $204.35   3.113%   $210.7114   $210.71   $210.70   $210.70  
  Purchase #2 $246.66   3.470%   $255.2191   $255.22   $255.20   $255.20  
  Purchase #3 $40.79   7.828%   $43.983   $43.98   $44.00   $44.00  
  Purchase #4 $136.34   7.231%   $146.1987   $146.20   $146.20   $146.20  
  Purchase #5 $230.36   7.825%   $248.3857   $248.39   $248.40   $248.40  
  Purchase #6 $218.64   9.399%   $239.19   $239.19   $239.20   $239.20  
  Purchase #7 $61.97   5.364%   $65.2941   $65.29   $65.30   $65.30  
  7 purchase totals = $1,139.11       $1,208.9820   $1,208.98   $1,209.00   $1,209.00