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 $204.94   7.147%   $219.5871   $219.59   $219.60   $219.60  
  Purchase #2 $70.79   4.425%   $73.9225   $73.92   $73.90   $73.90  
  Purchase #3 $243.87   7.730%   $262.7212   $262.72   $262.70   $262.70  
  Purchase #4 $115.58   6.451%   $123.0361   $123.04   $123.05   $123.00  
  Purchase #5 $86.74   8.477%   $94.0929   $94.09   $94.10   $94.10  
  Purchase #6 $87.81   10.325%   $96.8764   $96.88   $96.90   $96.90  
  Purchase #7 $227.33   6.800%   $242.7884   $242.79   $242.80   $242.80  
  7 purchase totals = $1,037.06       $1,113.0246   $1,113.03   $1,113.05   $1,113.00