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 $56.84   6.104%   $60.3095   $60.31   $60.30   $60.30  
  Purchase #2 $176.51   6.355%   $187.7272   $187.73   $187.75   $187.70  
  Purchase #3 $245.63   3.174%   $253.4263   $253.43   $253.45   $253.40  
  Purchase #4 $148.50   5.563%   $156.7611   $156.76   $156.75   $156.80  
  Purchase #5 $151.57   4.785%   $158.8226   $158.82   $158.80   $158.80  
  Purchase #6 $175.67   13.351%   $199.1237   $199.12   $199.10   $199.10  
  Purchase #7 $36.56   6.110%   $38.7938   $38.79   $38.80   $38.80  
  7 purchase totals = $991.28       $1,054.9642   $1,054.96   $1,054.95   $1,054.90