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 $60.66   8.402%   $65.7567   $65.76   $65.75   $65.80  
  Purchase #2 $234.28   5.821%   $247.9174   $247.92   $247.90   $247.90  
  Purchase #3 $16.52   9.295%   $18.0555   $18.06   $18.05   $18.10  
  Purchase #4 $43.91   7.510%   $47.2076   $47.21   $47.20   $47.20  
  Purchase #5 $84.94   13.391%   $96.3143   $96.31   $96.30   $96.30  
  Purchase #6 $132.52   10.421%   $146.3299   $146.33   $146.35   $146.30  
  Purchase #7 $117.41   5.343%   $123.6832   $123.68   $123.70   $123.70  
  7 purchase totals = $690.24       $745.2646   $745.27   $745.25   $745.30