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 $74.27   3.161%   $76.6177   $76.62   $76.60   $76.60  
  Purchase #2 $60.42   12.284%   $67.842   $67.84   $67.85   $67.80  
  Purchase #3 $66.34   3.704%   $68.7972   $68.80   $68.80   $68.80  
  Purchase #4 $18.26   8.346%   $19.784   $19.78   $19.80   $19.80  
  Purchase #5 $202.65   11.683%   $226.3256   $226.33   $226.35   $226.30  
  Purchase #6 $10.76   12.821%   $12.1395   $12.14   $12.15   $12.10  
  Purchase #7 $46.95   5.697%   $49.6247   $49.62   $49.60   $49.60  
  7 purchase totals = $479.65       $521.1307   $521.13   $521.15   $521.00