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 $60.32   8.106%   $65.2095   $65.21   $65.20   $65.20  
  Purchase #2 $104.25   10.606%   $115.3068   $115.31   $115.30   $115.30  
  Purchase #3 $88.62   5.286%   $93.3045   $93.30   $93.30   $93.30  
  Purchase #4 $126.56   5.178%   $133.1133   $133.11   $133.10   $133.10  
  Purchase #5 $96.97   8.610%   $105.3191   $105.32   $105.30   $105.30  
  Purchase #6 $187.80   5.806%   $198.7037   $198.70   $198.70   $198.70  
  Purchase #7 $108.84   7.158%   $116.6308   $116.63   $116.65   $116.60  
  7 purchase totals = $773.36       $827.5877   $827.58   $827.55   $827.50