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 $192.73   6.779%   $205.7952   $205.80   $205.80   $205.80  
  Purchase #2 $122.71   3.423%   $126.9104   $126.91   $126.90   $126.90  
  Purchase #3 $141.48   5.630%   $149.4453   $149.45   $149.45   $149.40  
  Purchase #4 $93.28   3.579%   $96.6185   $96.62   $96.60   $96.60  
  Purchase #5 $47.97   9.147%   $52.3578   $52.36   $52.35   $52.40  
  Purchase #6 $170.99   12.661%   $192.639   $192.64   $192.65   $192.60  
  Purchase #7 $124.87   4.285%   $130.2207   $130.22   $130.20   $130.20  
  7 purchase totals = $894.03       $953.9869   $954.00   $953.95   $953.90