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 $68.25   10.805%   $75.6244   $75.62   $75.60   $75.60  
  Purchase #2 $216.26   6.204%   $229.6768   $229.68   $229.70   $229.70  
  Purchase #3 $142.87   6.835%   $152.6352   $152.64   $152.65   $152.60  
  Purchase #4 $107.70   11.858%   $120.4711   $120.47   $120.45   $120.50  
  Purchase #5 $212.60   4.719%   $222.6326   $222.63   $222.65   $222.60  
  Purchase #6 $50.56   13.228%   $57.2481   $57.25   $57.25   $57.20  
  Purchase #7 $180.50   6.861%   $192.8841   $192.88   $192.90   $192.90  
  7 purchase totals = $978.74       $1,051.1723   $1,051.17   $1,051.20   $1,051.10