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 $232.54   12.834%   $262.3842   $262.38   $262.40   $262.40  
  Purchase #2 $17.97   4.129%   $18.712   $18.71   $18.70   $18.70  
  Purchase #3 $195.64   4.611%   $204.661   $204.66   $204.65   $204.70  
  Purchase #4 $141.50   4.135%   $147.351   $147.35   $147.35   $147.40  
  Purchase #5 $56.59   8.138%   $61.1953   $61.20   $61.20   $61.20  
  Purchase #6 $55.90   9.782%   $61.3681   $61.37   $61.35   $61.40  
  Purchase #7 $33.34   11.639%   $37.2204   $37.22   $37.20   $37.20  
  7 purchase totals = $733.48       $792.8920   $792.89   $792.85   $793.00