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 $108.32   13.155%   $122.5695   $122.57   $122.55   $122.60  
  Purchase #2 $214.36   7.693%   $230.8507   $230.85   $230.85   $230.90  
  Purchase #3 $173.97   11.857%   $194.5976   $194.60   $194.60   $194.60  
  Purchase #4 $129.55   3.549%   $134.1477   $134.15   $134.15   $134.10  
  Purchase #5 $68.73   8.692%   $74.704   $74.70   $74.70   $74.70  
  Purchase #6 $241.57   13.792%   $274.8873   $274.89   $274.90   $274.90  
  Purchase #7 $24.42   13.483%   $27.7125   $27.71   $27.70   $27.70  
  7 purchase totals = $960.92       $1,059.4693   $1,059.47   $1,059.45   $1,059.50