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 $84.42   9.698%   $92.6071   $92.61   $92.60   $92.60  
  Purchase #2 $246.51   13.461%   $279.6927   $279.69   $279.70   $279.70  
  Purchase #3 $176.26   13.657%   $200.3318   $200.33   $200.35   $200.30  
  Purchase #4 $150.28   7.844%   $162.068   $162.07   $162.05   $162.10  
  Purchase #5 $126.33   3.419%   $130.6492   $130.65   $130.65   $130.60  
  Purchase #6 $197.51   7.811%   $212.9375   $212.94   $212.95   $212.90  
  Purchase #7 $184.69   7.643%   $198.8059   $198.81   $198.80   $198.80  
  7 purchase totals = $1,166.00       $1,277.0922   $1,277.10   $1,277.10   $1,277.00