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 $61.60   3.758%   $63.9149   $63.91   $63.90   $63.90  
  Purchase #2 $58.96   12.871%   $66.5487   $66.55   $66.55   $66.50  
  Purchase #3 $236.81   3.143%   $244.2529   $244.25   $244.25   $244.30  
  Purchase #4 $228.62   6.169%   $242.7236   $242.72   $242.70   $242.70  
  Purchase #5 $7.87   3.242%   $8.1251   $8.13   $8.15   $8.10  
  Purchase #6 $117.37   5.110%   $123.3676   $123.37   $123.35   $123.40  
  Purchase #7 $201.79   8.427%   $218.7948   $218.79   $218.80   $218.80  
  7 purchase totals = $913.02       $967.7276   $967.72   $967.70   $967.70