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 $63.50   8.285%   $68.761   $68.76   $68.75   $68.80  
  Purchase #2 $146.83   11.450%   $163.642   $163.64   $163.65   $163.60  
  Purchase #3 $17.71   9.852%   $19.4548   $19.45   $19.45   $19.50  
  Purchase #4 $204.27   8.474%   $221.5798   $221.58   $221.60   $221.60  
  Purchase #5 $215.53   9.592%   $236.2036   $236.20   $236.20   $236.20  
  Purchase #6 $74.44   8.353%   $80.658   $80.66   $80.65   $80.70  
  Purchase #7 $116.69   8.611%   $126.7382   $126.74   $126.75   $126.70  
  7 purchase totals = $838.97       $917.0374   $917.03   $917.05   $917.10