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 $146.66   7.608%   $157.8179   $157.82   $157.80   $157.80  
  Purchase #2 $110.75   8.705%   $120.3908   $120.39   $120.40   $120.40  
  Purchase #3 $105.27   10.149%   $115.9539   $115.95   $115.95   $116.00  
  Purchase #4 $112.67   10.313%   $124.2897   $124.29   $124.30   $124.30  
  Purchase #5 $226.82   10.539%   $250.7246   $250.72   $250.70   $250.70  
  Purchase #6 $95.54   11.346%   $106.38   $106.38   $106.40   $106.40  
  Purchase #7 $129.73   9.228%   $141.7015   $141.70   $141.70   $141.70  
  7 purchase totals = $927.44       $1,017.2584   $1,017.25   $1,017.25   $1,017.30