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 $55.97   9.709%   $61.4041   $61.40   $61.40   $61.40  
  Purchase #2 $126.32   6.728%   $134.8188   $134.82   $134.80   $134.80  
  Purchase #3 $155.36   12.586%   $174.9136   $174.91   $174.90   $174.90  
  Purchase #4 $16.56   10.163%   $18.243   $18.24   $18.25   $18.20  
  Purchase #5 $119.72   13.717%   $136.142   $136.14   $136.15   $136.10  
  Purchase #6 $184.33   7.297%   $197.7806   $197.78   $197.80   $197.80  
  Purchase #7 $86.97   8.332%   $94.2163   $94.22   $94.20   $94.20  
  7 purchase totals = $745.23       $817.5184   $817.51   $817.50   $817.40