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 $92.59   13.463%   $105.0554   $105.06   $105.05   $105.10  
  Purchase #2 $136.83   13.757%   $155.6537   $155.65   $155.65   $155.70  
  Purchase #3 $179.73   6.655%   $191.691   $191.69   $191.70   $191.70  
  Purchase #4 $162.36   5.159%   $170.7362   $170.74   $170.75   $170.70  
  Purchase #5 $240.98   9.220%   $263.1984   $263.20   $263.20   $263.20  
  Purchase #6 $141.71   7.778%   $152.7322   $152.73   $152.75   $152.70  
  Purchase #7 $154.37   4.455%   $161.2472   $161.25   $161.25   $161.20  
  7 purchase totals = $1,108.57       $1,200.3141   $1,200.32   $1,200.35   $1,200.30