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 $233.96   8.288%   $253.3506   $253.35   $253.35   $253.40  
  Purchase #2 $179.56   12.826%   $202.5904   $202.59   $202.60   $202.60  
  Purchase #3 $147.73   12.202%   $165.756   $165.76   $165.75   $165.80  
  Purchase #4 $248.54   13.404%   $281.8543   $281.85   $281.85   $281.90  
  Purchase #5 $34.91   9.291%   $38.1535   $38.15   $38.15   $38.20  
  Purchase #6 $217.64   10.699%   $240.9253   $240.93   $240.95   $240.90  
  Purchase #7 $7.49   11.308%   $8.337   $8.34   $8.35   $8.30  
  7 purchase totals = $1,069.83       $1,190.9671   $1,190.97   $1,191.00   $1,191.10