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 $198.42   13.812%   $225.8258   $225.83   $225.85   $225.80  
  Purchase #2 $25.46   5.499%   $26.86   $26.86   $26.85   $26.90  
  Purchase #3 $173.47   7.196%   $185.9529   $185.95   $185.95   $186.00  
  Purchase #4 $158.97   8.212%   $172.0246   $172.02   $172.00   $172.00  
  Purchase #5 $219.65   4.213%   $228.9039   $228.90   $228.90   $228.90  
  Purchase #6 $8.67   13.635%   $9.8522   $9.85   $9.85   $9.90  
  Purchase #7 $113.92   8.492%   $123.5941   $123.59   $123.60   $123.60  
  7 purchase totals = $898.56       $973.0135   $973.00   $973.00   $973.10