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 $37.97   9.313%   $41.5061   $41.51   $41.50   $41.50  
  Purchase #2 $143.35   6.103%   $152.0987   $152.10   $152.10   $152.10  
  Purchase #3 $153.44   12.750%   $173.0036   $173.00   $173.00   $173.00  
  Purchase #4 $198.30   7.661%   $213.4918   $213.49   $213.50   $213.50  
  Purchase #5 $180.39   12.361%   $202.688   $202.69   $202.70   $202.70  
  Purchase #6 $132.93   3.402%   $137.4523   $137.45   $137.45   $137.50  
  Purchase #7 $233.28   9.411%   $255.234   $255.23   $255.25   $255.20  
  7 purchase totals = $1,079.66       $1,175.4745   $1,175.47   $1,175.50   $1,175.50