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 $197.69   13.621%   $224.6174   $224.62   $224.60   $224.60  
  Purchase #2 $41.76   9.226%   $45.6128   $45.61   $45.60   $45.60  
  Purchase #3 $244.86   7.713%   $263.7461   $263.75   $263.75   $263.70  
  Purchase #4 $84.90   12.648%   $95.6382   $95.64   $95.65   $95.60  
  Purchase #5 $214.71   12.232%   $240.9733   $240.97   $240.95   $241.00  
  Purchase #6 $157.71   6.481%   $167.9312   $167.93   $167.95   $167.90  
  Purchase #7 $185.41   3.287%   $191.5044   $191.50   $191.50   $191.50  
  7 purchase totals = $1,127.04       $1,230.0234   $1,230.02   $1,230.00   $1,229.90