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 $237.65   11.741%   $265.5525   $265.55   $265.55   $265.60  
  Purchase #2 $55.82   7.668%   $60.1003   $60.10   $60.10   $60.10  
  Purchase #3 $170.98   4.206%   $178.1714   $178.17   $178.15   $178.20  
  Purchase #4 $79.29   10.740%   $87.8057   $87.81   $87.80   $87.80  
  Purchase #5 $165.74   12.746%   $186.8652   $186.87   $186.85   $186.90  
  Purchase #6 $199.38   3.848%   $207.0521   $207.05   $207.05   $207.10  
  Purchase #7 $75.63   3.724%   $78.4465   $78.45   $78.45   $78.40  
  7 purchase totals = $984.49       $1,063.9937   $1,064.00   $1,063.95   $1,064.10