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 $47.92   13.701%   $54.4855   $54.49   $54.50   $54.50  
  Purchase #2 $231.42   7.426%   $248.6052   $248.61   $248.60   $248.60  
  Purchase #3 $162.27   4.125%   $168.9636   $168.96   $168.95   $169.00  
  Purchase #4 $189.96   5.199%   $199.836   $199.84   $199.85   $199.80  
  Purchase #5 $177.61   5.680%   $187.6982   $187.70   $187.70   $187.70  
  Purchase #6 $148.54   8.268%   $160.8213   $160.82   $160.80   $160.80  
  Purchase #7 $230.60   3.604%   $238.9108   $238.91   $238.90   $238.90  
  7 purchase totals = $1,188.32       $1,259.3206   $1,259.33   $1,259.30   $1,259.30