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 $236.62   12.403%   $265.968   $265.97   $265.95   $266.00  
  Purchase #2 $68.40   10.377%   $75.4979   $75.50   $75.50   $75.50  
  Purchase #3 $242.32   8.518%   $262.9608   $262.96   $262.95   $263.00  
  Purchase #4 $49.44   9.133%   $53.9554   $53.96   $53.95   $54.00  
  Purchase #5 $99.68   4.621%   $104.2862   $104.29   $104.30   $104.30  
  Purchase #6 $158.60   12.658%   $178.6756   $178.68   $178.70   $178.70  
  Purchase #7 $112.60   12.235%   $126.3766   $126.38   $126.40   $126.40  
  7 purchase totals = $967.66       $1,067.7205   $1,067.74   $1,067.75   $1,067.90