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 $93.84   9.830%   $103.0645   $103.06   $103.05   $103.10  
  Purchase #2 $91.86   4.788%   $96.2583   $96.26   $96.25   $96.30  
  Purchase #3 $119.80   13.811%   $136.3456   $136.35   $136.35   $136.30  
  Purchase #4 $57.32   11.633%   $63.988   $63.99   $64.00   $64.00  
  Purchase #5 $50.42   8.564%   $54.738   $54.74   $54.75   $54.70  
  Purchase #6 $77.42   11.693%   $86.4727   $86.47   $86.45   $86.50  
  Purchase #7 $48.55   11.616%   $54.1896   $54.19   $54.20   $54.20  
  7 purchase totals = $539.21       $595.0567   $595.06   $595.05   $595.10