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 $67.80   5.713%   $71.6734   $71.67   $71.65   $71.70  
  Purchase #2 $97.43   8.344%   $105.5596   $105.56   $105.55   $105.60  
  Purchase #3 $55.64   3.421%   $57.5434   $57.54   $57.55   $57.50  
  Purchase #4 $95.53   8.466%   $103.6176   $103.62   $103.60   $103.60  
  Purchase #5 $186.88   4.545%   $195.3737   $195.37   $195.35   $195.40  
  Purchase #6 $9.77   10.432%   $10.7892   $10.79   $10.80   $10.80  
  Purchase #7 $198.47   3.486%   $205.3887   $205.39   $205.40   $205.40  
  7 purchase totals = $711.52       $749.9456   $749.94   $749.90   $750.00