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 $208.52   8.256%   $225.7354   $225.74   $225.75   $225.70  
  Purchase #2 $39.63   5.379%   $41.7617   $41.76   $41.75   $41.80  
  Purchase #3 $237.63   8.517%   $257.8689   $257.87   $257.85   $257.90  
  Purchase #4 $249.57   10.572%   $275.9545   $275.95   $275.95   $276.00  
  Purchase #5 $30.79   7.564%   $33.119   $33.12   $33.10   $33.10  
  Purchase #6 $135.28   10.714%   $149.7739   $149.77   $149.75   $149.80  
  Purchase #7 $158.32   7.527%   $170.2367   $170.24   $170.25   $170.20  
  7 purchase totals = $1,059.74       $1,154.4501   $1,154.45   $1,154.40   $1,154.50