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 $232.31   13.284%   $263.1701   $263.17   $263.15   $263.20  
  Purchase #2 $93.67   12.251%   $105.1455   $105.15   $105.15   $105.10  
  Purchase #3 $162.66   9.714%   $178.4608   $178.46   $178.45   $178.50  
  Purchase #4 $141.30   10.552%   $156.21   $156.21   $156.20   $156.20  
  Purchase #5 $207.30   5.463%   $218.6248   $218.62   $218.60   $218.60  
  Purchase #6 $200.42   10.607%   $221.6785   $221.68   $221.70   $221.70  
  Purchase #7 $36.69   7.477%   $39.4333   $39.43   $39.45   $39.40  
  7 purchase totals = $1,074.35       $1,182.7230   $1,182.72   $1,182.70   $1,182.70