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 $235.68   5.690%   $249.0902   $249.09   $249.10   $249.10  
  Purchase #2 $61.98   8.423%   $67.2006   $67.20   $67.20   $67.20  
  Purchase #3 $136.33   6.427%   $145.0919   $145.09   $145.10   $145.10  
  Purchase #4 $154.98   8.178%   $167.6543   $167.65   $167.65   $167.70  
  Purchase #5 $115.51   13.636%   $131.2609   $131.26   $131.25   $131.30  
  Purchase #6 $148.58   6.157%   $157.7281   $157.73   $157.75   $157.70  
  Purchase #7 $219.48   6.622%   $234.014   $234.01   $234.00   $234.00  
  7 purchase totals = $1,072.54       $1,152.0400   $1,152.03   $1,152.05   $1,152.10