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 $120.91   3.670%   $125.3474   $125.35   $125.35   $125.30  
  Purchase #2 $136.45   10.337%   $150.5548   $150.55   $150.55   $150.60  
  Purchase #3 $26.92   11.310%   $29.9647   $29.96   $29.95   $30.00  
  Purchase #4 $250.62   3.350%   $259.0158   $259.02   $259.00   $259.00  
  Purchase #5 $87.68   7.611%   $94.3533   $94.35   $94.35   $94.40  
  Purchase #6 $162.42   4.120%   $169.1117   $169.11   $169.10   $169.10  
  Purchase #7 $230.32   11.717%   $257.3066   $257.31   $257.30   $257.30  
  7 purchase totals = $1,015.32       $1,085.6543   $1,085.65   $1,085.60   $1,085.70