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 $226.51   12.656%   $255.1771   $255.18   $255.20   $255.20  
  Purchase #2 $172.68   11.182%   $191.9891   $191.99   $192.00   $192.00  
  Purchase #3 $150.56   9.772%   $165.2727   $165.27   $165.25   $165.30  
  Purchase #4 $248.61   6.160%   $263.9244   $263.92   $263.90   $263.90  
  Purchase #5 $219.30   6.455%   $233.4558   $233.46   $233.45   $233.50  
  Purchase #6 $247.27   4.235%   $257.7419   $257.74   $257.75   $257.70  
  Purchase #7 $88.65   8.456%   $96.1462   $96.15   $96.15   $96.10  
  7 purchase totals = $1,353.58       $1,463.7072   $1,463.71   $1,463.70   $1,463.70