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 $203.35   3.142%   $209.7393   $209.74   $209.75   $209.70  
  Purchase #2 $186.39   8.593%   $202.4065   $202.41   $202.40   $202.40  
  Purchase #3 $159.95   10.573%   $176.8615   $176.86   $176.85   $176.90  
  Purchase #4 $225.57   10.119%   $248.3954   $248.40   $248.40   $248.40  
  Purchase #5 $45.89   12.313%   $51.5404   $51.54   $51.55   $51.50  
  Purchase #6 $213.73   9.789%   $234.652   $234.65   $234.65   $234.70  
  Purchase #7 $190.82   4.838%   $200.0519   $200.05   $200.05   $200.10  
  7 purchase totals = $1,225.70       $1,323.6470   $1,323.65   $1,323.65   $1,323.70