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 $184.81   8.437%   $200.4024   $200.40   $200.40   $200.40  
  Purchase #2 $166.75   13.308%   $188.9411   $188.94   $188.95   $188.90  
  Purchase #3 $50.39   7.608%   $54.2237   $54.22   $54.20   $54.20  
  Purchase #4 $226.53   3.415%   $234.266   $234.27   $234.25   $234.30  
  Purchase #5 $239.93   4.341%   $250.3454   $250.35   $250.35   $250.30  
  Purchase #6 $235.74   5.506%   $248.7198   $248.72   $248.70   $248.70  
  Purchase #7 $189.27   13.260%   $214.3672   $214.37   $214.35   $214.40  
  7 purchase totals = $1,293.42       $1,391.2656   $1,391.27   $1,391.20   $1,391.20