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 $20.30   7.125%   $21.7464   $21.75   $21.75   $21.70  
  Purchase #2 $135.80   5.110%   $142.7394   $142.74   $142.75   $142.70  
  Purchase #3 $145.60   12.838%   $164.2921   $164.29   $164.30   $164.30  
  Purchase #4 $168.97   10.385%   $186.5175   $186.52   $186.50   $186.50  
  Purchase #5 $140.68   10.273%   $155.1321   $155.13   $155.15   $155.10  
  Purchase #6 $156.57   5.286%   $164.8463   $164.85   $164.85   $164.80  
  Purchase #7 $123.80   3.856%   $128.5737   $128.57   $128.55   $128.60  
  7 purchase totals = $891.72       $963.8475   $963.85   $963.85   $963.70