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 $186.70   4.312%   $194.7505   $194.75   $194.75   $194.80  
  Purchase #2 $122.58   8.367%   $132.8363   $132.84   $132.85   $132.80  
  Purchase #3 $172.75   11.624%   $192.8305   $192.83   $192.85   $192.80  
  Purchase #4 $248.64   10.222%   $274.056   $274.06   $274.05   $274.10  
  Purchase #5 $73.78   4.856%   $77.3628   $77.36   $77.35   $77.40  
  Purchase #6 $106.33   9.337%   $116.258   $116.26   $116.25   $116.30  
  Purchase #7 $227.71   6.363%   $242.1992   $242.20   $242.20   $242.20  
  7 purchase totals = $1,138.49       $1,230.2933   $1,230.30   $1,230.30   $1,230.40