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 $237.31   13.737%   $269.9093   $269.91   $269.90   $269.90  
  Purchase #2 $96.44   6.800%   $102.9979   $103.00   $103.00   $103.00  
  Purchase #3 $165.51   12.260%   $185.8015   $185.80   $185.80   $185.80  
  Purchase #4 $202.89   4.321%   $211.6569   $211.66   $211.65   $211.70  
  Purchase #5 $235.72   12.864%   $266.043   $266.04   $266.05   $266.00  
  Purchase #6 $161.36   6.198%   $171.3611   $171.36   $171.35   $171.40  
  Purchase #7 $183.48   5.466%   $193.509   $193.51   $193.50   $193.50  
  7 purchase totals = $1,282.71       $1,401.2787   $1,401.28   $1,401.25   $1,401.30