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 $37.38   9.846%   $41.0604   $41.06   $41.05   $41.10  
  Purchase #2 $125.79   13.405%   $142.6521   $142.65   $142.65   $142.70  
  Purchase #3 $142.38   9.481%   $155.879   $155.88   $155.90   $155.90  
  Purchase #4 $154.38   3.105%   $159.1735   $159.17   $159.15   $159.20  
  Purchase #5 $239.89   10.391%   $264.817   $264.82   $264.80   $264.80  
  Purchase #6 $144.54   13.439%   $163.9647   $163.96   $163.95   $164.00  
  Purchase #7 $129.54   3.836%   $134.5092   $134.51   $134.50   $134.50  
  7 purchase totals = $973.90       $1,062.0559   $1,062.05   $1,062.00   $1,062.20