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 $214.65   10.107%   $236.3447   $236.34   $236.35   $236.30  
  Purchase #2 $192.26   12.689%   $216.6559   $216.66   $216.65   $216.70  
  Purchase #3 $34.94   8.171%   $37.7949   $37.79   $37.80   $37.80  
  Purchase #4 $227.50   8.569%   $246.9945   $246.99   $247.00   $247.00  
  Purchase #5 $241.48   13.408%   $273.8576   $273.86   $273.85   $273.90  
  Purchase #6 $24.34   6.228%   $25.8559   $25.86   $25.85   $25.90  
  Purchase #7 $85.46   12.860%   $96.4502   $96.45   $96.45   $96.50  
  7 purchase totals = $1,020.63       $1,133.9537   $1,133.95   $1,133.95   $1,134.10