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 $181.38   13.350%   $205.5942   $205.59   $205.60   $205.60  
  Purchase #2 $221.32   5.153%   $232.7246   $232.72   $232.70   $232.70  
  Purchase #3 $123.55   6.477%   $131.5523   $131.55   $131.55   $131.60  
  Purchase #4 $246.88   13.493%   $280.1915   $280.19   $280.20   $280.20  
  Purchase #5 $204.61   3.803%   $212.3913   $212.39   $212.40   $212.40  
  Purchase #6 $129.53   4.626%   $135.5221   $135.52   $135.50   $135.50  
  Purchase #7 $248.80   10.380%   $274.6254   $274.63   $274.65   $274.60  
  7 purchase totals = $1,356.07       $1,472.6014   $1,472.59   $1,472.60   $1,472.60