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 $236.58   4.261%   $246.6607   $246.66   $246.65   $246.70  
  Purchase #2 $121.79   4.496%   $127.2657   $127.27   $127.25   $127.30  
  Purchase #3 $62.36   4.396%   $65.1013   $65.10   $65.10   $65.10  
  Purchase #4 $216.55   11.434%   $241.3103   $241.31   $241.30   $241.30  
  Purchase #5 $214.86   7.636%   $231.2667   $231.27   $231.25   $231.30  
  Purchase #6 $184.92   3.535%   $191.4569   $191.46   $191.45   $191.50  
  Purchase #7 $155.97   3.569%   $161.5366   $161.54   $161.55   $161.50  
  7 purchase totals = $1,193.03       $1,264.5982   $1,264.61   $1,264.55   $1,264.70