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 $32.53   10.602%   $35.9788   $35.98   $36.00   $36.00  
  Purchase #2 $176.53   6.340%   $187.722   $187.72   $187.70   $187.70  
  Purchase #3 $22.60   8.693%   $24.5646   $24.56   $24.55   $24.60  
  Purchase #4 $163.85   7.523%   $176.1764   $176.18   $176.20   $176.20  
  Purchase #5 $155.48   11.401%   $173.2063   $173.21   $173.20   $173.20  
  Purchase #6 $147.88   6.839%   $157.9935   $157.99   $158.00   $158.00  
  Purchase #7 $232.52   6.385%   $247.3664   $247.37   $247.35   $247.40  
  7 purchase totals = $931.39       $1,003.0080   $1,003.01   $1,003.00   $1,003.10