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 $244.38   9.674%   $268.0213   $268.02   $268.00   $268.00  
  Purchase #2 $206.48   8.615%   $224.2683   $224.27   $224.25   $224.30  
  Purchase #3 $82.53   6.124%   $87.5841   $87.58   $87.60   $87.60  
  Purchase #4 $143.59   13.426%   $162.8684   $162.87   $162.85   $162.90  
  Purchase #5 $131.28   12.466%   $147.6454   $147.65   $147.65   $147.60  
  Purchase #6 $212.28   12.655%   $239.144   $239.14   $239.15   $239.10  
  Purchase #7 $202.49   4.395%   $211.3894   $211.39   $211.40   $211.40  
  7 purchase totals = $1,223.03       $1,340.9209   $1,340.92   $1,340.90   $1,340.90