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 $156.91   13.285%   $177.7555   $177.76   $177.75   $177.80  
  Purchase #2 $85.37   8.545%   $92.6649   $92.66   $92.65   $92.70  
  Purchase #3 $109.72   8.813%   $119.3896   $119.39   $119.40   $119.40  
  Purchase #4 $231.44   12.121%   $259.4928   $259.49   $259.50   $259.50  
  Purchase #5 $201.58   6.818%   $215.3237   $215.32   $215.30   $215.30  
  Purchase #6 $65.28   12.756%   $73.6071   $73.61   $73.60   $73.60  
  Purchase #7 $75.43   13.742%   $85.7956   $85.80   $85.80   $85.80  
  7 purchase totals = $925.73       $1,024.0292   $1,024.03   $1,024.00   $1,024.10