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 $61.82   10.143%   $68.0904   $68.09   $68.10   $68.10  
  Purchase #2 $238.62   8.545%   $259.0101   $259.01   $259.00   $259.00  
  Purchase #3 $50.47   4.614%   $52.7987   $52.80   $52.80   $52.80  
  Purchase #4 $86.48   11.525%   $96.4468   $96.45   $96.45   $96.40  
  Purchase #5 $102.25   4.256%   $106.6018   $106.60   $106.60   $106.60  
  Purchase #6 $81.73   4.793%   $85.6473   $85.65   $85.65   $85.60  
  Purchase #7 $210.88   8.125%   $228.014   $228.01   $228.00   $228.00  
  7 purchase totals = $832.25       $896.6091   $896.61   $896.60   $896.50