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 $171.84   13.204%   $194.5298   $194.53   $194.55   $194.50  
  Purchase #2 $64.78   4.868%   $67.9335   $67.93   $67.95   $67.90  
  Purchase #3 $159.87   5.659%   $168.917   $168.92   $168.90   $168.90  
  Purchase #4 $56.53   6.258%   $60.0676   $60.07   $60.05   $60.10  
  Purchase #5 $55.45   8.815%   $60.3379   $60.34   $60.35   $60.30  
  Purchase #6 $230.88   7.627%   $248.4892   $248.49   $248.50   $248.50  
  Purchase #7 $250.90   12.313%   $281.7933   $281.79   $281.80   $281.80  
  7 purchase totals = $990.25       $1,082.0683   $1,082.07   $1,082.10   $1,082.00