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 $62.62   5.618%   $66.138   $66.14   $66.15   $66.10  
  Purchase #2 $61.84   7.538%   $66.5015   $66.50   $66.50   $66.50  
  Purchase #3 $59.40   10.337%   $65.5402   $65.54   $65.55   $65.50  
  Purchase #4 $202.73   5.751%   $214.389   $214.39   $214.40   $214.40  
  Purchase #5 $15.65   6.836%   $16.7198   $16.72   $16.70   $16.70  
  Purchase #6 $155.36   6.656%   $165.7008   $165.70   $165.70   $165.70  
  Purchase #7 $184.44   9.651%   $202.2403   $202.24   $202.25   $202.20  
  7 purchase totals = $742.04       $797.2296   $797.23   $797.25   $797.10