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 $162.61   12.116%   $182.3118   $182.31   $182.30   $182.30  
  Purchase #2 $140.94   8.382%   $152.7536   $152.75   $152.75   $152.80  
  Purchase #3 $205.29   8.713%   $223.1769   $223.18   $223.20   $223.20  
  Purchase #4 $213.43   13.436%   $242.1065   $242.11   $242.10   $242.10  
  Purchase #5 $5.33   6.465%   $5.6746   $5.67   $5.65   $5.70  
  Purchase #6 $171.26   5.287%   $180.3145   $180.31   $180.30   $180.30  
  Purchase #7 $132.83   9.344%   $145.2416   $145.24   $145.25   $145.20  
  7 purchase totals = $1,031.69       $1,131.5795   $1,131.57   $1,131.55   $1,131.60