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 $41.97   10.368%   $46.3214   $46.32   $46.30   $46.30  
  Purchase #2 $164.95   10.839%   $182.8289   $182.83   $182.85   $182.80  
  Purchase #3 $125.41   13.293%   $142.0808   $142.08   $142.10   $142.10  
  Purchase #4 $146.33   6.783%   $156.2556   $156.26   $156.25   $156.30  
  Purchase #5 $200.57   10.394%   $221.4172   $221.42   $221.40   $221.40  
  Purchase #6 $5.66   12.351%   $6.3591   $6.36   $6.35   $6.40  
  Purchase #7 $246.77   10.442%   $272.5377   $272.54   $272.55   $272.50  
  7 purchase totals = $931.66       $1,027.8007   $1,027.81   $1,027.80   $1,027.80