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 $111.87   5.651%   $118.1918   $118.19   $118.20   $118.20  
  Purchase #2 $207.58   9.622%   $227.5533   $227.55   $227.55   $227.60  
  Purchase #3 $87.62   12.782%   $98.8196   $98.82   $98.80   $98.80  
  Purchase #4 $243.28   5.658%   $257.0448   $257.04   $257.05   $257.00  
  Purchase #5 $130.46   4.256%   $136.0124   $136.01   $136.00   $136.00  
  Purchase #6 $171.45   7.414%   $184.1613   $184.16   $184.15   $184.20  
  Purchase #7 $51.98   9.713%   $57.0288   $57.03   $57.05   $57.00  
  7 purchase totals = $1,004.24       $1,078.8120   $1,078.80   $1,078.80   $1,078.80