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 $57.98   6.479%   $61.7365   $61.74   $61.75   $61.70  
  Purchase #2 $108.88   5.216%   $114.5592   $114.56   $114.55   $114.60  
  Purchase #3 $141.97   10.222%   $156.4822   $156.48   $156.50   $156.50  
  Purchase #4 $54.77   6.806%   $58.4976   $58.50   $58.50   $58.50  
  Purchase #5 $105.61   3.772%   $109.5936   $109.59   $109.60   $109.60  
  Purchase #6 $157.59   3.460%   $163.0426   $163.04   $163.05   $163.00  
  Purchase #7 $79.82   4.496%   $83.4087   $83.41   $83.40   $83.40  
  7 purchase totals = $706.62       $747.3204   $747.32   $747.35   $747.30