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 $226.70   5.141%   $238.3546   $238.35   $238.35   $238.40  
  Purchase #2 $248.39   10.429%   $274.2946   $274.29   $274.30   $274.30  
  Purchase #3 $119.61   6.402%   $127.2674   $127.27   $127.25   $127.30  
  Purchase #4 $76.62   4.380%   $79.976   $79.98   $80.00   $80.00  
  Purchase #5 $115.95   5.460%   $122.2809   $122.28   $122.30   $122.30  
  Purchase #6 $225.47   7.230%   $241.7715   $241.77   $241.75   $241.80  
  Purchase #7 $58.25   11.645%   $65.0332   $65.03   $65.05   $65.00  
  7 purchase totals = $1,070.99       $1,148.9782   $1,148.97   $1,149.00   $1,149.10