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 $244.74   7.269%   $262.5302   $262.53   $262.55   $262.50  
  Purchase #2 $75.67   7.730%   $81.5193   $81.52   $81.50   $81.50  
  Purchase #3 $158.51   5.861%   $167.8003   $167.80   $167.80   $167.80  
  Purchase #4 $248.77   12.142%   $278.9757   $278.98   $279.00   $279.00  
  Purchase #5 $73.30   9.480%   $80.2488   $80.25   $80.25   $80.20  
  Purchase #6 $146.76   6.820%   $156.769   $156.77   $156.75   $156.80  
  Purchase #7 $29.55   9.576%   $32.3797   $32.38   $32.40   $32.40  
  7 purchase totals = $977.30       $1,060.2230   $1,060.23   $1,060.25   $1,060.20