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 $65.51   7.321%   $70.306   $70.31   $70.30   $70.30  
  Purchase #2 $15.93   6.763%   $17.0073   $17.01   $17.00   $17.00  
  Purchase #3 $58.92   13.623%   $66.9467   $66.95   $66.95   $66.90  
  Purchase #4 $86.61   7.173%   $92.8225   $92.82   $92.80   $92.80  
  Purchase #5 $194.82   6.609%   $207.6957   $207.70   $207.70   $207.70  
  Purchase #6 $116.63   5.466%   $123.005   $123.01   $123.00   $123.00  
  Purchase #7 $157.81   7.612%   $169.8225   $169.82   $169.80   $169.80  
  7 purchase totals = $696.23       $747.6057   $747.62   $747.55   $747.50