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 $95.61   10.866%   $105.999   $106.00   $106.00   $106.00  
  Purchase #2 $230.60   5.117%   $242.3998   $242.40   $242.40   $242.40  
  Purchase #3 $35.37   9.344%   $38.675   $38.68   $38.70   $38.70  
  Purchase #4 $41.83   9.456%   $45.7854   $45.79   $45.80   $45.80  
  Purchase #5 $130.64   8.310%   $141.4962   $141.50   $141.50   $141.50  
  Purchase #6 $240.50   10.232%   $265.108   $265.11   $265.10   $265.10  
  Purchase #7 $76.80   6.741%   $81.9771   $81.98   $82.00   $82.00  
  7 purchase totals = $851.35       $921.4405   $921.46   $921.50   $921.50