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 $205.77   9.699%   $225.7276   $225.73   $225.75   $225.70  
  Purchase #2 $148.89   7.376%   $159.8721   $159.87   $159.85   $159.90  
  Purchase #3 $196.64   9.639%   $215.5941   $215.59   $215.60   $215.60  
  Purchase #4 $147.64   4.318%   $154.0151   $154.02   $154.00   $154.00  
  Purchase #5 $131.54   6.190%   $139.6823   $139.68   $139.70   $139.70  
  Purchase #6 $174.28   12.353%   $195.8088   $195.81   $195.80   $195.80  
  Purchase #7 $165.73   11.606%   $184.9646   $184.96   $184.95   $185.00  
  7 purchase totals = $1,170.49       $1,275.6646   $1,275.66   $1,275.65   $1,275.70