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 $55.98   9.399%   $61.2416   $61.24   $61.25   $61.20  
  Purchase #2 $179.95   7.158%   $192.8308   $192.83   $192.85   $192.80  
  Purchase #3 $103.30   8.215%   $111.7861   $111.79   $111.80   $111.80  
  Purchase #4 $145.99   11.122%   $162.227   $162.23   $162.25   $162.20  
  Purchase #5 $190.39   6.403%   $202.5807   $202.58   $202.60   $202.60  
  Purchase #6 $68.90   8.106%   $74.485   $74.49   $74.50   $74.50  
  Purchase #7 $40.43   7.842%   $43.6005   $43.60   $43.60   $43.60  
  7 purchase totals = $784.94       $848.7517   $848.76   $848.85   $848.70