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 $111.94   6.463%   $119.1747   $119.17   $119.15   $119.20  
  Purchase #2 $119.93   10.197%   $132.1593   $132.16   $132.15   $132.20  
  Purchase #3 $194.86   4.798%   $204.2094   $204.21   $204.20   $204.20  
  Purchase #4 $248.93   10.367%   $274.7366   $274.74   $274.75   $274.70  
  Purchase #5 $224.58   12.689%   $253.077   $253.08   $253.10   $253.10  
  Purchase #6 $242.86   8.768%   $264.154   $264.15   $264.15   $264.20  
  Purchase #7 $249.42   7.870%   $269.0494   $269.05   $269.05   $269.00  
  7 purchase totals = $1,392.52       $1,516.5604   $1,516.56   $1,516.55   $1,516.60