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 $53.87   12.739%   $60.7325   $60.73   $60.75   $60.70  
  Purchase #2 $227.79   10.395%   $251.4688   $251.47   $251.45   $251.50  
  Purchase #3 $218.41   6.809%   $233.2815   $233.28   $233.30   $233.30  
  Purchase #4 $240.74   9.860%   $264.477   $264.48   $264.50   $264.50  
  Purchase #5 $140.82   9.188%   $153.7585   $153.76   $153.75   $153.80  
  Purchase #6 $138.43   3.651%   $143.4841   $143.48   $143.50   $143.50  
  Purchase #7 $189.78   4.637%   $198.5801   $198.58   $198.60   $198.60  
  7 purchase totals = $1,209.84       $1,305.7825   $1,305.78   $1,305.85   $1,305.90