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 $210.28   6.402%   $223.7421   $223.74   $223.75   $223.70  
  Purchase #2 $124.39   12.249%   $139.6265   $139.63   $139.65   $139.60  
  Purchase #3 $60.79   5.632%   $64.2137   $64.21   $64.20   $64.20  
  Purchase #4 $175.50   5.666%   $185.4438   $185.44   $185.45   $185.40  
  Purchase #5 $100.80   9.466%   $110.3417   $110.34   $110.35   $110.30  
  Purchase #6 $203.63   3.834%   $211.4372   $211.44   $211.45   $211.40  
  Purchase #7 $70.27   4.833%   $73.6661   $73.67   $73.65   $73.70  
  7 purchase totals = $945.66       $1,008.4711   $1,008.47   $1,008.50   $1,008.30