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 $108.83   7.133%   $116.5928   $116.59   $116.60   $116.60  
  Purchase #2 $192.76   6.641%   $205.5612   $205.56   $205.55   $205.60  
  Purchase #3 $174.88   11.870%   $195.6383   $195.64   $195.65   $195.60  
  Purchase #4 $34.41   5.346%   $36.2496   $36.25   $36.25   $36.20  
  Purchase #5 $85.32   12.572%   $96.0464   $96.05   $96.05   $96.00  
  Purchase #6 $48.94   12.112%   $54.8676   $54.87   $54.85   $54.90  
  Purchase #7 $188.94   6.541%   $201.2986   $201.30   $201.30   $201.30  
  7 purchase totals = $834.08       $906.2545   $906.26   $906.25   $906.20