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 $81.57   8.190%   $88.2506   $88.25   $88.25   $88.30  
  Purchase #2 $8.37   5.669%   $8.8445   $8.84   $8.85   $8.80  
  Purchase #3 $169.96   5.292%   $178.9543   $178.95   $178.95   $179.00  
  Purchase #4 $91.39   11.282%   $101.7006   $101.70   $101.70   $101.70  
  Purchase #5 $101.85   7.353%   $109.339   $109.34   $109.35   $109.30  
  Purchase #6 $54.34   12.262%   $61.0032   $61.00   $61.00   $61.00  
  Purchase #7 $168.63   4.547%   $176.2976   $176.30   $176.30   $176.30  
  7 purchase totals = $676.11       $724.3898   $724.38   $724.40   $724.40