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 $48.59   8.698%   $52.8164   $52.82   $52.80   $52.80  
  Purchase #2 $214.70   12.395%   $241.3121   $241.31   $241.30   $241.30  
  Purchase #3 $105.96   9.547%   $116.076   $116.08   $116.10   $116.10  
  Purchase #4 $249.39   4.830%   $261.4355   $261.44   $261.45   $261.40  
  Purchase #5 $34.99   11.693%   $39.0814   $39.08   $39.10   $39.10  
  Purchase #6 $192.32   5.452%   $202.8053   $202.81   $202.80   $202.80  
  Purchase #7 $233.74   7.155%   $250.4641   $250.46   $250.45   $250.50  
  7 purchase totals = $1,079.69       $1,163.9908   $1,164.00   $1,164.00   $1,164.00