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 $156.38   4.671%   $163.6845   $163.68   $163.70   $163.70  
  Purchase #2 $173.41   5.722%   $183.3325   $183.33   $183.35   $183.30  
  Purchase #3 $95.71   11.866%   $107.0669   $107.07   $107.05   $107.10  
  Purchase #4 $229.34   6.206%   $243.5728   $243.57   $243.55   $243.60  
  Purchase #5 $54.36   7.707%   $58.5495   $58.55   $58.55   $58.50  
  Purchase #6 $84.44   11.614%   $94.2469   $94.25   $94.25   $94.20  
  Purchase #7 $189.68   9.243%   $207.2121   $207.21   $207.20   $207.20  
  7 purchase totals = $983.32       $1,057.6652   $1,057.66   $1,057.65   $1,057.60