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 $70.47   8.601%   $76.5311   $76.53   $76.55   $76.50  
  Purchase #2 $122.98   10.564%   $135.9716   $135.97   $135.95   $136.00  
  Purchase #3 $234.29   11.748%   $261.8144   $261.81   $261.80   $261.80  
  Purchase #4 $177.65   10.221%   $195.8076   $195.81   $195.80   $195.80  
  Purchase #5 $188.39   5.468%   $198.6912   $198.69   $198.70   $198.70  
  Purchase #6 $102.37   7.780%   $110.3344   $110.33   $110.35   $110.30  
  Purchase #7 $216.70   4.445%   $226.3323   $226.33   $226.35   $226.30  
  7 purchase totals = $1,112.85       $1,205.4826   $1,205.47   $1,205.50   $1,205.40