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 $56.83   9.141%   $62.0248   $62.02   $62.00   $62.00  
  Purchase #2 $184.59   5.837%   $195.3645   $195.36   $195.35   $195.40  
  Purchase #3 $140.59   6.211%   $149.322   $149.32   $149.30   $149.30  
  Purchase #4 $245.98   13.831%   $280.0015   $280.00   $280.00   $280.00  
  Purchase #5 $67.70   4.794%   $70.9455   $70.95   $70.95   $70.90  
  Purchase #6 $130.83   12.812%   $147.5919   $147.59   $147.60   $147.60  
  Purchase #7 $155.44   13.787%   $176.8705   $176.87   $176.85   $176.90  
  7 purchase totals = $981.96       $1,082.1207   $1,082.11   $1,082.05   $1,082.10