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 $114.55   4.285%   $119.4585   $119.46   $119.45   $119.50  
  Purchase #2 $59.99   8.474%   $65.0736   $65.07   $65.05   $65.10  
  Purchase #3 $128.60   7.234%   $137.9029   $137.90   $137.90   $137.90  
  Purchase #4 $231.49   5.149%   $243.4094   $243.41   $243.40   $243.40  
  Purchase #5 $104.42   10.209%   $115.0802   $115.08   $115.10   $115.10  
  Purchase #6 $83.62   4.528%   $87.4063   $87.41   $87.40   $87.40  
  Purchase #7 $161.80   12.523%   $182.0622   $182.06   $182.05   $182.10  
  7 purchase totals = $884.47       $950.3931   $950.39   $950.35   $950.50