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 $214.44   13.869%   $244.1807   $244.18   $244.20   $244.20  
  Purchase #2 $109.93   11.800%   $122.9017   $122.90   $122.90   $122.90  
  Purchase #3 $33.83   11.518%   $37.7265   $37.73   $37.75   $37.70  
  Purchase #4 $137.66   3.298%   $142.2   $142.20   $142.20   $142.20  
  Purchase #5 $136.35   3.167%   $140.6682   $140.67   $140.65   $140.70  
  Purchase #6 $147.38   9.592%   $161.5167   $161.52   $161.50   $161.50  
  Purchase #7 $220.97   4.181%   $230.2088   $230.21   $230.20   $230.20  
  7 purchase totals = $1,000.56       $1,079.4026   $1,079.41   $1,079.40   $1,079.40