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 $24.53   8.198%   $26.541   $26.54   $26.55   $26.50  
  Purchase #2 $142.55   4.347%   $148.7466   $148.75   $148.75   $148.70  
  Purchase #3 $61.95   8.293%   $67.0875   $67.09   $67.10   $67.10  
  Purchase #4 $27.27   12.390%   $30.6488   $30.65   $30.65   $30.60  
  Purchase #5 $60.71   11.733%   $67.8331   $67.83   $67.85   $67.80  
  Purchase #6 $22.30   8.171%   $24.1221   $24.12   $24.10   $24.10  
  Purchase #7 $183.29   6.579%   $195.3486   $195.35   $195.35   $195.30  
  7 purchase totals = $522.60       $560.3277   $560.33   $560.35   $560.10