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 $144.90   4.619%   $151.5929   $151.59   $151.60   $151.60  
  Purchase #2 $218.77   7.712%   $235.6415   $235.64   $235.65   $235.60  
  Purchase #3 $74.63   12.407%   $83.8893   $83.89   $83.90   $83.90  
  Purchase #4 $95.87   13.277%   $108.5987   $108.60   $108.60   $108.60  
  Purchase #5 $157.61   13.586%   $179.0229   $179.02   $179.00   $179.00  
  Purchase #6 $117.36   6.113%   $124.5342   $124.53   $124.55   $124.50  
  Purchase #7 $55.44   9.381%   $60.6408   $60.64   $60.65   $60.60  
  7 purchase totals = $864.58       $943.9203   $943.91   $943.95   $943.80