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 $118.70   8.466%   $128.7491   $128.75   $128.75   $128.70  
  Purchase #2 $57.37   9.299%   $62.7048   $62.70   $62.70   $62.70  
  Purchase #3 $60.32   12.774%   $68.0253   $68.03   $68.05   $68.00  
  Purchase #4 $208.44   8.442%   $226.0365   $226.04   $226.05   $226.00  
  Purchase #5 $91.53   13.735%   $104.1016   $104.10   $104.10   $104.10  
  Purchase #6 $222.88   6.253%   $236.8167   $236.82   $236.80   $236.80  
  Purchase #7 $163.85   10.612%   $181.2378   $181.24   $181.25   $181.20  
  7 purchase totals = $923.09       $1,007.6718   $1,007.68   $1,007.70   $1,007.50