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 $86.36   5.667%   $91.254   $91.25   $91.25   $91.30  
  Purchase #2 $69.49   6.821%   $74.2299   $74.23   $74.25   $74.20  
  Purchase #3 $192.51   6.505%   $205.0328   $205.03   $205.05   $205.00  
  Purchase #4 $126.92   3.482%   $131.3394   $131.34   $131.35   $131.30  
  Purchase #5 $240.30   10.641%   $265.8703   $265.87   $265.85   $265.90  
  Purchase #6 $32.86   6.547%   $35.0113   $35.01   $35.00   $35.00  
  Purchase #7 $120.89   6.514%   $128.7648   $128.76   $128.75   $128.80  
  7 purchase totals = $869.33       $931.5025   $931.49   $931.50   $931.50