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 $23.52   10.574%   $26.007   $26.01   $26.00   $26.00  
  Purchase #2 $6.63   13.201%   $7.5052   $7.51   $7.50   $7.50  
  Purchase #3 $26.48   9.222%   $28.922   $28.92   $28.90   $28.90  
  Purchase #4 $236.74   13.611%   $268.9627   $268.96   $268.95   $269.00  
  Purchase #5 $73.51   10.559%   $81.2719   $81.27   $81.25   $81.30  
  Purchase #6 $77.27   11.488%   $86.1468   $86.15   $86.15   $86.10  
  Purchase #7 $89.30   5.311%   $94.0427   $94.04   $94.05   $94.00  
  7 purchase totals = $533.45       $592.8583   $592.86   $592.80   $592.80