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 $168.99   11.617%   $188.6216   $188.62   $188.60   $188.60  
  Purchase #2 $47.47   13.616%   $53.9335   $53.93   $53.95   $53.90  
  Purchase #3 $90.99   9.656%   $99.776   $99.78   $99.80   $99.80  
  Purchase #4 $51.68   9.133%   $56.3999   $56.40   $56.40   $56.40  
  Purchase #5 $100.29   7.116%   $107.4266   $107.43   $107.45   $107.40  
  Purchase #6 $141.58   10.175%   $155.9858   $155.99   $156.00   $156.00  
  Purchase #7 $93.33   9.431%   $102.132   $102.13   $102.15   $102.10  
  7 purchase totals = $694.33       $764.2754   $764.28   $764.35   $764.20