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 $38.88   11.440%   $43.3279   $43.33   $43.35   $43.30  
  Purchase #2 $31.27   4.104%   $32.5533   $32.55   $32.55   $32.60  
  Purchase #3 $131.51   11.166%   $146.1944   $146.19   $146.20   $146.20  
  Purchase #4 $246.90   12.743%   $278.3625   $278.36   $278.35   $278.40  
  Purchase #5 $198.63   5.845%   $210.2399   $210.24   $210.25   $210.20  
  Purchase #6 $213.72   6.212%   $226.9963   $227.00   $227.00   $227.00  
  Purchase #7 $153.91   6.317%   $163.6325   $163.63   $163.65   $163.60  
  7 purchase totals = $1,014.82       $1,101.3068   $1,101.30   $1,101.35   $1,101.30