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 $185.37   10.180%   $204.2407   $204.24   $204.25   $204.20  
  Purchase #2 $230.91   13.268%   $261.5471   $261.55   $261.55   $261.50  
  Purchase #3 $114.45   13.531%   $129.9362   $129.94   $129.95   $129.90  
  Purchase #4 $204.52   11.432%   $227.9007   $227.90   $227.90   $227.90  
  Purchase #5 $228.37   10.195%   $251.6523   $251.65   $251.65   $251.70  
  Purchase #6 $40.40   8.235%   $43.7269   $43.73   $43.75   $43.70  
  Purchase #7 $214.85   7.186%   $230.2891   $230.29   $230.30   $230.30  
  7 purchase totals = $1,218.87       $1,349.2930   $1,349.30   $1,349.35   $1,349.20