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 $56.88   6.733%   $60.7097   $60.71   $60.70   $60.70  
  Purchase #2 $224.35   9.523%   $245.7149   $245.71   $245.70   $245.70  
  Purchase #3 $139.88   8.851%   $152.2608   $152.26   $152.25   $152.30  
  Purchase #4 $173.88   8.834%   $189.2406   $189.24   $189.25   $189.20  
  Purchase #5 $67.56   5.143%   $71.0346   $71.03   $71.05   $71.00  
  Purchase #6 $197.41   13.205%   $223.478   $223.48   $223.50   $223.50  
  Purchase #7 $187.90   5.377%   $198.0034   $198.00   $198.00   $198.00  
  7 purchase totals = $1,047.86       $1,140.4420   $1,140.43   $1,140.45   $1,140.40