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 $116.85   8.207%   $126.4399   $126.44   $126.45   $126.40  
  Purchase #2 $235.72   13.539%   $267.6341   $267.63   $267.65   $267.60  
  Purchase #3 $113.43   3.470%   $117.366   $117.37   $117.35   $117.40  
  Purchase #4 $134.94   8.165%   $145.9579   $145.96   $145.95   $146.00  
  Purchase #5 $208.54   8.342%   $225.9364   $225.94   $225.95   $225.90  
  Purchase #6 $133.51   7.339%   $143.3083   $143.31   $143.30   $143.30  
  Purchase #7 $26.93   6.256%   $28.6147   $28.61   $28.60   $28.60  
  7 purchase totals = $969.92       $1,055.2573   $1,055.26   $1,055.25   $1,055.20