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 $211.80   10.440%   $233.9119   $233.91   $233.90   $233.90  
  Purchase #2 $166.69   9.465%   $182.4672   $182.47   $182.45   $182.50  
  Purchase #3 $229.33   4.347%   $239.299   $239.30   $239.30   $239.30  
  Purchase #4 $175.58   5.113%   $184.5574   $184.56   $184.55   $184.60  
  Purchase #5 $159.25   8.746%   $173.178   $173.18   $173.20   $173.20  
  Purchase #6 $231.43   13.415%   $262.4763   $262.48   $262.50   $262.50  
  Purchase #7 $118.92   8.217%   $128.6917   $128.69   $128.70   $128.70  
  7 purchase totals = $1,293.00       $1,404.5815   $1,404.59   $1,404.60   $1,404.70