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 $246.52   3.252%   $254.5368   $254.54   $254.55   $254.50  
  Purchase #2 $164.95   6.662%   $175.939   $175.94   $175.95   $175.90  
  Purchase #3 $144.52   4.169%   $150.545   $150.55   $150.55   $150.50  
  Purchase #4 $154.90   8.807%   $168.542   $168.54   $168.55   $168.50  
  Purchase #5 $238.99   5.291%   $251.635   $251.64   $251.65   $251.60  
  Purchase #6 $229.54   13.663%   $260.9021   $260.90   $260.90   $260.90  
  Purchase #7 $16.75   4.809%   $17.5555   $17.56   $17.55   $17.60  
  7 purchase totals = $1,196.17       $1,279.6554   $1,279.67   $1,279.70   $1,279.50