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 $63.70   11.873%   $71.2631   $71.26   $71.25   $71.30  
  Purchase #2 $201.33   6.110%   $213.6313   $213.63   $213.65   $213.60  
  Purchase #3 $110.64   5.503%   $116.7285   $116.73   $116.75   $116.70  
  Purchase #4 $173.78   3.451%   $179.7771   $179.78   $179.80   $179.80  
  Purchase #5 $76.96   12.479%   $86.5638   $86.56   $86.55   $86.60  
  Purchase #6 $246.27   7.147%   $263.8709   $263.87   $263.85   $263.90  
  Purchase #7 $36.70   8.473%   $39.8096   $39.81   $39.80   $39.80  
  7 purchase totals = $909.38       $971.6443   $971.64   $971.65   $971.70