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 $61.67   5.511%   $65.0686   $65.07   $65.05   $65.10  
  Purchase #2 $109.60   7.349%   $117.6545   $117.65   $117.65   $117.70  
  Purchase #3 $34.25   7.635%   $36.865   $36.87   $36.85   $36.90  
  Purchase #4 $205.52   8.532%   $223.055   $223.06   $223.05   $223.10  
  Purchase #5 $82.48   13.118%   $93.2997   $93.30   $93.30   $93.30  
  Purchase #6 $42.89   11.123%   $47.6607   $47.66   $47.65   $47.70  
  Purchase #7 $139.37   8.393%   $151.0673   $151.07   $151.05   $151.10  
  7 purchase totals = $675.78       $734.6708   $734.68   $734.60   $734.90