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 $198.33   13.318%   $224.7436   $224.74   $224.75   $224.70  
  Purchase #2 $85.87   6.652%   $91.5821   $91.58   $91.60   $91.60  
  Purchase #3 $44.35   5.354%   $46.7245   $46.72   $46.70   $46.70  
  Purchase #4 $89.46   4.502%   $93.4875   $93.49   $93.50   $93.50  
  Purchase #5 $242.27   11.251%   $269.5278   $269.53   $269.55   $269.50  
  Purchase #6 $171.44   9.595%   $187.8897   $187.89   $187.90   $187.90  
  Purchase #7 $79.65   6.172%   $84.566   $84.57   $84.55   $84.60  
  7 purchase totals = $911.37       $998.5212   $998.52   $998.55   $998.50