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 $171.77   13.627%   $195.1771   $195.18   $195.20   $195.20  
  Purchase #2 $39.40   6.462%   $41.946   $41.95   $41.95   $41.90  
  Purchase #3 $149.25   5.352%   $157.2379   $157.24   $157.25   $157.20  
  Purchase #4 $40.68   5.716%   $43.0053   $43.01   $43.00   $43.00  
  Purchase #5 $188.98   6.379%   $201.035   $201.04   $201.05   $201.00  
  Purchase #6 $171.59   13.332%   $194.4664   $194.47   $194.45   $194.50  
  Purchase #7 $235.76   5.577%   $248.9083   $248.91   $248.90   $248.90  
  7 purchase totals = $997.43       $1,081.7760   $1,081.80   $1,081.80   $1,081.70