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 $112.64   9.411%   $123.2406   $123.24   $123.25   $123.20  
  Purchase #2 $188.42   8.588%   $204.6015   $204.60   $204.60   $204.60  
  Purchase #3 $106.33   11.674%   $118.743   $118.74   $118.75   $118.70  
  Purchase #4 $201.53   6.136%   $213.8959   $213.90   $213.90   $213.90  
  Purchase #5 $235.85   13.470%   $267.619   $267.62   $267.60   $267.60  
  Purchase #6 $26.51   5.162%   $27.8784   $27.88   $27.90   $27.90  
  Purchase #7 $164.36   6.257%   $174.644   $174.64   $174.65   $174.60  
  7 purchase totals = $1,035.64       $1,130.6224   $1,130.62   $1,130.65   $1,130.50