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 $225.81   11.242%   $251.1956   $251.20   $251.20   $251.20  
  Purchase #2 $113.37   8.755%   $123.2955   $123.30   $123.30   $123.30  
  Purchase #3 $76.83   6.717%   $81.9907   $81.99   $82.00   $82.00  
  Purchase #4 $125.68   5.104%   $132.0947   $132.09   $132.10   $132.10  
  Purchase #5 $160.59   10.531%   $177.5017   $177.50   $177.50   $177.50  
  Purchase #6 $243.40   10.760%   $269.5898   $269.59   $269.60   $269.60  
  Purchase #7 $196.91   7.720%   $212.1115   $212.11   $212.10   $212.10  
  7 purchase totals = $1,142.59       $1,247.7795   $1,247.78   $1,247.80   $1,247.80