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 $41.85   6.229%   $44.4568   $44.46   $44.45   $44.50  
  Purchase #2 $211.42   9.582%   $231.6783   $231.68   $231.70   $231.70  
  Purchase #3 $168.72   10.749%   $186.8557   $186.86   $186.85   $186.90  
  Purchase #4 $30.69   6.502%   $32.6855   $32.69   $32.70   $32.70  
  Purchase #5 $90.87   6.495%   $96.772   $96.77   $96.75   $96.80  
  Purchase #6 $55.72   5.778%   $58.9395   $58.94   $58.95   $58.90  
  Purchase #7 $224.83   7.618%   $241.9575   $241.96   $241.95   $242.00  
  7 purchase totals = $824.10       $893.3453   $893.36   $893.35   $893.50