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 $85.52   10.824%   $94.7767   $94.78   $94.80   $94.80  
  Purchase #2 $240.80   12.609%   $271.1625   $271.16   $271.15   $271.20  
  Purchase #3 $234.74   11.695%   $262.1928   $262.19   $262.20   $262.20  
  Purchase #4 $36.68   7.684%   $39.4985   $39.50   $39.50   $39.50  
  Purchase #5 $79.67   7.199%   $85.4054   $85.41   $85.40   $85.40  
  Purchase #6 $88.87   3.790%   $92.2382   $92.24   $92.25   $92.20  
  Purchase #7 $144.55   12.728%   $162.9483   $162.95   $162.95   $162.90  
  7 purchase totals = $910.83       $1,008.2224   $1,008.23   $1,008.25   $1,008.20