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 $246.96   5.176%   $259.7426   $259.74   $259.75   $259.70  
  Purchase #2 $200.59   3.274%   $207.1573   $207.16   $207.15   $207.20  
  Purchase #3 $74.83   9.679%   $82.0728   $82.07   $82.05   $82.10  
  Purchase #4 $113.99   11.732%   $127.3633   $127.36   $127.35   $127.40  
  Purchase #5 $239.33   8.254%   $259.0843   $259.08   $259.10   $259.10  
  Purchase #6 $250.27   11.396%   $278.7908   $278.79   $278.80   $278.80  
  Purchase #7 $242.38   10.726%   $268.3777   $268.38   $268.40   $268.40  
  7 purchase totals = $1,368.35       $1,482.5888   $1,482.58   $1,482.60   $1,482.70