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 $90.99   5.349%   $95.8571   $95.86   $95.85   $95.90  
  Purchase #2 $77.91   11.326%   $86.7341   $86.73   $86.75   $86.70  
  Purchase #3 $212.70   13.634%   $241.6995   $241.70   $241.70   $241.70  
  Purchase #4 $26.39   5.287%   $27.7852   $27.79   $27.80   $27.80  
  Purchase #5 $164.64   3.571%   $170.5193   $170.52   $170.50   $170.50  
  Purchase #6 $161.35   12.247%   $181.1105   $181.11   $181.10   $181.10  
  Purchase #7 $101.47   8.106%   $109.6952   $109.70   $109.70   $109.70  
  7 purchase totals = $835.45       $913.4009   $913.41   $913.40   $913.40