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 $201.78   12.424%   $226.8491   $226.85   $226.85   $226.80  
  Purchase #2 $225.58   3.868%   $234.3054   $234.31   $234.30   $234.30  
  Purchase #3 $137.42   11.421%   $153.1147   $153.11   $153.10   $153.10  
  Purchase #4 $223.36   13.129%   $252.6849   $252.68   $252.70   $252.70  
  Purchase #5 $250.95   6.274%   $266.6946   $266.69   $266.70   $266.70  
  Purchase #6 $151.34   9.163%   $165.2073   $165.21   $165.20   $165.20  
  Purchase #7 $83.94   13.135%   $94.9655   $94.97   $94.95   $95.00  
  7 purchase totals = $1,274.37       $1,393.8215   $1,393.82   $1,393.80   $1,393.80