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 $24.33   8.198%   $26.3246   $26.32   $26.30   $26.30  
  Purchase #2 $200.59   12.473%   $225.6096   $225.61   $225.60   $225.60  
  Purchase #3 $32.60   11.133%   $36.2294   $36.23   $36.25   $36.20  
  Purchase #4 $198.93   3.213%   $205.3216   $205.32   $205.30   $205.30  
  Purchase #5 $196.46   8.664%   $213.4813   $213.48   $213.50   $213.50  
  Purchase #6 $177.75   6.751%   $189.7499   $189.75   $189.75   $189.70  
  Purchase #7 $91.40   5.107%   $96.0678   $96.07   $96.05   $96.10  
  7 purchase totals = $922.06       $992.7842   $992.78   $992.75   $992.70