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 $62.38   7.460%   $67.0335   $67.03   $67.05   $67.00  
  Purchase #2 $72.66   5.442%   $76.6142   $76.61   $76.60   $76.60  
  Purchase #3 $145.77   8.323%   $157.9024   $157.90   $157.90   $157.90  
  Purchase #4 $162.46   7.172%   $174.1116   $174.11   $174.10   $174.10  
  Purchase #5 $95.43   9.381%   $104.3823   $104.38   $104.40   $104.40  
  Purchase #6 $121.44   6.121%   $128.8733   $128.87   $128.85   $128.90  
  Purchase #7 $114.89   8.603%   $124.774   $124.77   $124.75   $124.80  
  7 purchase totals = $775.03       $833.6913   $833.67   $833.65   $833.70