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 $178.73   5.164%   $187.9596   $187.96   $187.95   $188.00  
  Purchase #2 $86.91   4.160%   $90.5255   $90.53   $90.55   $90.50  
  Purchase #3 $100.25   6.452%   $106.7181   $106.72   $106.70   $106.70  
  Purchase #4 $240.25   8.235%   $260.0346   $260.03   $260.05   $260.00  
  Purchase #5 $26.97   8.626%   $29.2964   $29.30   $29.30   $29.30  
  Purchase #6 $181.53   13.725%   $206.445   $206.45   $206.45   $206.40  
  Purchase #7 $132.50   6.686%   $141.359   $141.36   $141.35   $141.40  
  7 purchase totals = $947.14       $1,022.3382   $1,022.35   $1,022.35   $1,022.30