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 $101.95   10.843%   $113.0044   $113.00   $113.00   $113.00  
  Purchase #2 $171.70   9.706%   $188.3652   $188.37   $188.35   $188.40  
  Purchase #3 $176.54   8.799%   $192.0738   $192.07   $192.05   $192.10  
  Purchase #4 $176.32   9.865%   $193.714   $193.71   $193.70   $193.70  
  Purchase #5 $83.97   5.783%   $88.826   $88.83   $88.85   $88.80  
  Purchase #6 $187.88   3.424%   $194.313   $194.31   $194.30   $194.30  
  Purchase #7 $72.55   7.401%   $77.9194   $77.92   $77.90   $77.90  
  7 purchase totals = $970.91       $1,048.2158   $1,048.21   $1,048.15   $1,048.20