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 $200.86   10.143%   $221.2332   $221.23   $221.25   $221.20  
  Purchase #2 $25.65   4.602%   $26.8304   $26.83   $26.85   $26.80  
  Purchase #3 $154.33   3.529%   $159.7763   $159.78   $159.80   $159.80  
  Purchase #4 $68.96   4.130%   $71.808   $71.81   $71.80   $71.80  
  Purchase #5 $204.82   7.637%   $220.4621   $220.46   $220.45   $220.50  
  Purchase #6 $215.76   5.759%   $228.1856   $228.19   $228.20   $228.20  
  Purchase #7 $140.84   4.257%   $146.8356   $146.84   $146.85   $146.80  
  7 purchase totals = $1,011.22       $1,075.1312   $1,075.14   $1,075.20   $1,075.10