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 $133.91   5.503%   $141.2791   $141.28   $141.30   $141.30  
  Purchase #2 $116.61   8.797%   $126.8682   $126.87   $126.85   $126.90  
  Purchase #3 $184.64   12.363%   $207.467   $207.47   $207.45   $207.50  
  Purchase #4 $240.38   11.823%   $268.8001   $268.80   $268.80   $268.80  
  Purchase #5 $75.40   4.595%   $78.8646   $78.86   $78.85   $78.90  
  Purchase #6 $60.47   11.206%   $67.2463   $67.25   $67.25   $67.20  
  Purchase #7 $66.81   6.167%   $70.9302   $70.93   $70.95   $70.90  
  7 purchase totals = $878.22       $961.4555   $961.46   $961.45   $961.50