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 $81.65   13.611%   $92.7634   $92.76   $92.75   $92.80  
  Purchase #2 $146.54   11.815%   $163.8537   $163.85   $163.85   $163.90  
  Purchase #3 $36.98   11.675%   $41.2974   $41.30   $41.30   $41.30  
  Purchase #4 $194.74   12.661%   $219.396   $219.40   $219.40   $219.40  
  Purchase #5 $83.35   10.187%   $91.8409   $91.84   $91.85   $91.80  
  Purchase #6 $48.88   11.175%   $54.3423   $54.34   $54.35   $54.30  
  Purchase #7 $122.98   5.551%   $129.8066   $129.81   $129.80   $129.80  
  7 purchase totals = $715.12       $793.3003   $793.30   $793.30   $793.30