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 $210.44   6.368%   $223.8408   $223.84   $223.85   $223.80  
  Purchase #2 $233.53   11.721%   $260.9021   $260.90   $260.90   $260.90  
  Purchase #3 $239.64   13.154%   $271.1622   $271.16   $271.15   $271.20  
  Purchase #4 $82.52   13.323%   $93.5141   $93.51   $93.50   $93.50  
  Purchase #5 $71.42   6.396%   $75.988   $75.99   $76.00   $76.00  
  Purchase #6 $250.25   5.322%   $263.5683   $263.57   $263.55   $263.60  
  Purchase #7 $101.95   5.823%   $107.8865   $107.89   $107.90   $107.90  
  7 purchase totals = $1,189.75       $1,296.8620   $1,296.86   $1,296.85   $1,296.90