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 $154.81   8.232%   $167.554   $167.55   $167.55   $167.60  
  Purchase #2 $158.68   4.204%   $165.3509   $165.35   $165.35   $165.40  
  Purchase #3 $83.69   6.141%   $88.8294   $88.83   $88.85   $88.80  
  Purchase #4 $44.33   4.616%   $46.3763   $46.38   $46.40   $46.40  
  Purchase #5 $43.42   5.730%   $45.908   $45.91   $45.90   $45.90  
  Purchase #6 $193.59   5.584%   $204.4001   $204.40   $204.40   $204.40  
  Purchase #7 $196.28   4.255%   $204.6317   $204.63   $204.65   $204.60  
  7 purchase totals = $874.80       $923.0504   $923.05   $923.10   $923.10