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 $233.59   8.525%   $253.5035   $253.50   $253.50   $253.50  
  Purchase #2 $211.37   6.424%   $224.9484   $224.95   $224.95   $224.90  
  Purchase #3 $13.73   8.222%   $14.8589   $14.86   $14.85   $14.90  
  Purchase #4 $240.75   12.457%   $270.7402   $270.74   $270.75   $270.70  
  Purchase #5 $175.65   8.253%   $190.1464   $190.15   $190.15   $190.10  
  Purchase #6 $224.76   13.348%   $254.761   $254.76   $254.75   $254.80  
  Purchase #7 $117.37   8.440%   $127.276   $127.28   $127.30   $127.30  
  7 purchase totals = $1,217.22       $1,336.2344   $1,336.24   $1,336.25   $1,336.20