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 $108.67   6.752%   $116.0074   $116.01   $116.00   $116.00  
  Purchase #2 $177.43   12.191%   $199.0605   $199.06   $199.05   $199.10  
  Purchase #3 $242.49   4.161%   $252.58   $252.58   $252.60   $252.60  
  Purchase #4 $93.43   13.234%   $105.7945   $105.79   $105.80   $105.80  
  Purchase #5 $183.67   4.770%   $192.4311   $192.43   $192.45   $192.40  
  Purchase #6 $127.47   8.118%   $137.818   $137.82   $137.80   $137.80  
  Purchase #7 $145.89   13.536%   $165.6377   $165.64   $165.65   $165.60  
  7 purchase totals = $1,079.05       $1,169.3292   $1,169.33   $1,169.35   $1,169.30