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 $187.96   9.228%   $205.3049   $205.30   $205.30   $205.30  
  Purchase #2 $241.34   7.696%   $259.9135   $259.91   $259.90   $259.90  
  Purchase #3 $203.91   12.292%   $228.9746   $228.97   $228.95   $229.00  
  Purchase #4 $159.30   9.684%   $174.7266   $174.73   $174.75   $174.70  
  Purchase #5 $89.58   6.338%   $95.2576   $95.26   $95.25   $95.30  
  Purchase #6 $247.76   6.170%   $263.0468   $263.05   $263.05   $263.00  
  Purchase #7 $110.84   13.359%   $125.6471   $125.65   $125.65   $125.60  
  7 purchase totals = $1,240.69       $1,352.8711   $1,352.87   $1,352.85   $1,352.80