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 $140.61   6.854%   $150.2474   $150.25   $150.25   $150.20  
  Purchase #2 $23.36   8.133%   $25.2599   $25.26   $25.25   $25.30  
  Purchase #3 $248.32   11.481%   $276.8296   $276.83   $276.85   $276.80  
  Purchase #4 $73.96   13.450%   $83.9076   $83.91   $83.90   $83.90  
  Purchase #5 $192.95   5.862%   $204.2607   $204.26   $204.25   $204.30  
  Purchase #6 $249.70   7.361%   $268.0804   $268.08   $268.10   $268.10  
  Purchase #7 $55.45   9.535%   $60.7372   $60.74   $60.75   $60.70  
  7 purchase totals = $984.35       $1,069.3228   $1,069.33   $1,069.35   $1,069.30