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 $216.78   10.276%   $239.0563   $239.06   $239.05   $239.10  
  Purchase #2 $98.55   8.236%   $106.6666   $106.67   $106.65   $106.70  
  Purchase #3 $238.48   3.559%   $246.9675   $246.97   $246.95   $247.00  
  Purchase #4 $170.56   8.476%   $185.0167   $185.02   $185.00   $185.00  
  Purchase #5 $214.73   3.805%   $222.9005   $222.90   $222.90   $222.90  
  Purchase #6 $192.29   13.865%   $218.951   $218.95   $218.95   $219.00  
  Purchase #7 $38.93   7.729%   $41.9389   $41.94   $41.95   $41.90  
  7 purchase totals = $1,170.32       $1,261.4975   $1,261.51   $1,261.45   $1,261.60