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 $155.58   13.866%   $177.1527   $177.15   $177.15   $177.20  
  Purchase #2 $168.33   7.704%   $181.2981   $181.30   $181.30   $181.30  
  Purchase #3 $83.78   3.634%   $86.8246   $86.82   $86.80   $86.80  
  Purchase #4 $192.99   3.393%   $199.5382   $199.54   $199.55   $199.50  
  Purchase #5 $51.79   6.694%   $55.2568   $55.26   $55.25   $55.30  
  Purchase #6 $153.26   11.305%   $170.586   $170.59   $170.60   $170.60  
  Purchase #7 $144.92   3.699%   $150.2806   $150.28   $150.30   $150.30  
  7 purchase totals = $950.65       $1,020.9370   $1,020.94   $1,020.95   $1,021.00