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 $206.84   8.814%   $225.0709   $225.07   $225.05   $225.10  
  Purchase #2 $94.78   9.758%   $104.0286   $104.03   $104.05   $104.00  
  Purchase #3 $222.89   11.869%   $249.3448   $249.34   $249.35   $249.30  
  Purchase #4 $119.68   6.773%   $127.7859   $127.79   $127.80   $127.80  
  Purchase #5 $204.31   10.357%   $225.4704   $225.47   $225.45   $225.50  
  Purchase #6 $122.53   8.283%   $132.6792   $132.68   $132.70   $132.70  
  Purchase #7 $211.59   3.788%   $219.605   $219.61   $219.60   $219.60  
  7 purchase totals = $1,182.62       $1,283.9848   $1,283.99   $1,284.00   $1,284.00