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 $85.97   10.795%   $95.2505   $95.25   $95.25   $95.30  
  Purchase #2 $130.46   7.860%   $140.7142   $140.71   $140.70   $140.70  
  Purchase #3 $34.54   12.549%   $38.8744   $38.87   $38.85   $38.90  
  Purchase #4 $199.96   13.512%   $226.9786   $226.98   $227.00   $227.00  
  Purchase #5 $28.25   4.559%   $29.5379   $29.54   $29.55   $29.50  
  Purchase #6 $89.60   9.673%   $98.267   $98.27   $98.25   $98.30  
  Purchase #7 $166.39   5.657%   $175.8027   $175.80   $175.80   $175.80  
  7 purchase totals = $735.17       $805.4253   $805.42   $805.40   $805.50