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 $126.57   6.627%   $134.9578   $134.96   $134.95   $135.00  
  Purchase #2 $164.38   11.222%   $182.8267   $182.83   $182.85   $182.80  
  Purchase #3 $158.81   11.276%   $176.7174   $176.72   $176.70   $176.70  
  Purchase #4 $195.85   6.435%   $208.4529   $208.45   $208.45   $208.50  
  Purchase #5 $90.40   4.210%   $94.2058   $94.21   $94.20   $94.20  
  Purchase #6 $59.86   3.771%   $62.1173   $62.12   $62.10   $62.10  
  Purchase #7 $82.35   6.185%   $87.4433   $87.44   $87.45   $87.40  
  7 purchase totals = $878.22       $946.7212   $946.73   $946.70   $946.70