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 $183.47   9.582%   $201.0501   $201.05   $201.05   $201.10  
  Purchase #2 $208.58   10.873%   $231.2589   $231.26   $231.25   $231.30  
  Purchase #3 $204.41   6.862%   $218.4366   $218.44   $218.45   $218.40  
  Purchase #4 $9.62   10.707%   $10.65   $10.65   $10.65   $10.70  
  Purchase #5 $66.49   3.196%   $68.615   $68.62   $68.60   $68.60  
  Purchase #6 $224.80   10.457%   $248.3073   $248.31   $248.30   $248.30  
  Purchase #7 $247.90   7.346%   $266.1107   $266.11   $266.10   $266.10  
  7 purchase totals = $1,145.27       $1,244.4286   $1,244.44   $1,244.40   $1,244.50