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 $87.69   12.568%   $98.7109   $98.71   $98.70   $98.70  
  Purchase #2 $195.27   6.333%   $207.6364   $207.64   $207.65   $207.60  
  Purchase #3 $64.30   6.394%   $68.4113   $68.41   $68.40   $68.40  
  Purchase #4 $77.46   9.241%   $84.6181   $84.62   $84.60   $84.60  
  Purchase #5 $136.78   4.527%   $142.972   $142.97   $142.95   $143.00  
  Purchase #6 $235.71   11.222%   $262.1614   $262.16   $262.15   $262.20  
  Purchase #7 $138.45   8.514%   $150.2376   $150.24   $150.25   $150.20  
  7 purchase totals = $935.66       $1,014.7477   $1,014.75   $1,014.70   $1,014.70