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 $90.81   5.337%   $95.6565   $95.66   $95.65   $95.70  
  Purchase #2 $26.48   12.719%   $29.848   $29.85   $29.85   $29.80  
  Purchase #3 $126.34   7.839%   $136.2438   $136.24   $136.25   $136.20  
  Purchase #4 $59.99   7.582%   $64.5384   $64.54   $64.55   $64.50  
  Purchase #5 $127.94   8.363%   $138.6396   $138.64   $138.65   $138.60  
  Purchase #6 $213.94   3.307%   $221.015   $221.02   $221.00   $221.00  
  Purchase #7 $24.47   4.794%   $25.6431   $25.64   $25.65   $25.60  
  7 purchase totals = $669.97       $711.5844   $711.59   $711.60   $711.40