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 $165.58   5.258%   $174.2862   $174.29   $174.30   $174.30  
  Purchase #2 $239.55   13.564%   $272.0426   $272.04   $272.05   $272.00  
  Purchase #3 $121.30   9.337%   $132.6258   $132.63   $132.65   $132.60  
  Purchase #4 $247.64   4.127%   $257.8601   $257.86   $257.85   $257.90  
  Purchase #5 $37.36   10.292%   $41.2051   $41.21   $41.20   $41.20  
  Purchase #6 $167.87   3.789%   $174.2306   $174.23   $174.25   $174.20  
  Purchase #7 $230.41   13.757%   $262.1075   $262.11   $262.10   $262.10  
  7 purchase totals = $1,209.71       $1,314.3579   $1,314.37   $1,314.40   $1,314.30