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 $57.43   4.501%   $60.0149   $60.01   $60.00   $60.00  
  Purchase #2 $162.34   4.595%   $169.7995   $169.80   $169.80   $169.80  
  Purchase #3 $234.33   4.672%   $245.2779   $245.28   $245.30   $245.30  
  Purchase #4 $184.99   13.441%   $209.8545   $209.85   $209.85   $209.90  
  Purchase #5 $209.59   13.583%   $238.0586   $238.06   $238.05   $238.10  
  Purchase #6 $197.37   6.767%   $210.726   $210.73   $210.75   $210.70  
  Purchase #7 $87.79   5.863%   $92.9371   $92.94   $92.95   $92.90  
  7 purchase totals = $1,133.84       $1,226.6685   $1,226.67   $1,226.70   $1,226.70