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 $231.64   5.238%   $243.7733   $243.77   $243.75   $243.80  
  Purchase #2 $224.66   11.738%   $251.0306   $251.03   $251.05   $251.00  
  Purchase #3 $65.97   3.856%   $68.5138   $68.51   $68.50   $68.50  
  Purchase #4 $174.34   9.109%   $190.2206   $190.22   $190.20   $190.20  
  Purchase #5 $219.85   9.152%   $239.9707   $239.97   $239.95   $240.00  
  Purchase #6 $240.90   12.300%   $270.5307   $270.53   $270.55   $270.50  
  Purchase #7 $185.29   9.364%   $202.6406   $202.64   $202.65   $202.60  
  7 purchase totals = $1,342.65       $1,466.6803   $1,466.67   $1,466.65   $1,466.60