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 $215.83   8.657%   $234.5144   $234.51   $234.50   $234.50  
  Purchase #2 $136.97   5.166%   $144.0459   $144.05   $144.05   $144.00  
  Purchase #3 $108.68   4.425%   $113.4891   $113.49   $113.50   $113.50  
  Purchase #4 $61.64   4.735%   $64.5587   $64.56   $64.55   $64.60  
  Purchase #5 $232.85   5.560%   $245.7965   $245.80   $245.80   $245.80  
  Purchase #6 $124.42   5.654%   $131.4547   $131.45   $131.45   $131.50  
  Purchase #7 $73.61   8.472%   $79.8462   $79.85   $79.85   $79.80  
  7 purchase totals = $954.00       $1,013.7055   $1,013.71   $1,013.70   $1,013.70