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 $104.31   9.796%   $114.5282   $114.53   $114.55   $114.50  
  Purchase #2 $155.42   12.487%   $174.8273   $174.83   $174.85   $174.80  
  Purchase #3 $18.60   11.553%   $20.7489   $20.75   $20.75   $20.70  
  Purchase #4 $138.69   4.449%   $144.8603   $144.86   $144.85   $144.90  
  Purchase #5 $67.46   3.620%   $69.9021   $69.90   $69.90   $69.90  
  Purchase #6 $197.60   3.239%   $204.0003   $204.00   $204.00   $204.00  
  Purchase #7 $24.57   7.118%   $26.3189   $26.32   $26.30   $26.30  
  7 purchase totals = $706.65       $755.1860   $755.19   $755.20   $755.10