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 $166.56   11.486%   $185.6911   $185.69   $185.70   $185.70  
  Purchase #2 $211.82   5.613%   $223.7095   $223.71   $223.70   $223.70  
  Purchase #3 $223.70   13.193%   $253.2127   $253.21   $253.20   $253.20  
  Purchase #4 $39.64   9.420%   $43.3741   $43.37   $43.35   $43.40  
  Purchase #5 $174.80   7.665%   $188.1984   $188.20   $188.20   $188.20  
  Purchase #6 $58.29   11.243%   $64.8435   $64.84   $64.85   $64.80  
  Purchase #7 $250.25   8.517%   $271.5638   $271.56   $271.55   $271.60  
  7 purchase totals = $1,125.06       $1,230.5931   $1,230.58   $1,230.55   $1,230.60