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 $91.27   5.716%   $96.487   $96.49   $96.50   $96.50  
  Purchase #2 $14.29   3.578%   $14.8013   $14.80   $14.80   $14.80  
  Purchase #3 $129.68   7.457%   $139.3502   $139.35   $139.35   $139.40  
  Purchase #4 $235.61   11.479%   $262.6557   $262.66   $262.65   $262.70  
  Purchase #5 $36.42   9.693%   $39.9502   $39.95   $39.95   $40.00  
  Purchase #6 $187.64   9.812%   $206.0512   $206.05   $206.05   $206.10  
  Purchase #7 $213.41   11.185%   $237.2799   $237.28   $237.30   $237.30  
  7 purchase totals = $908.32       $996.5755   $996.58   $996.60   $996.80