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 $205.86   7.577%   $221.458   $221.46   $221.45   $221.50  
  Purchase #2 $165.45   11.256%   $184.0731   $184.07   $184.05   $184.10  
  Purchase #3 $197.43   4.194%   $205.7102   $205.71   $205.70   $205.70  
  Purchase #4 $82.39   6.451%   $87.705   $87.71   $87.70   $87.70  
  Purchase #5 $86.67   9.596%   $94.9869   $94.99   $95.00   $95.00  
  Purchase #6 $150.86   7.250%   $161.7974   $161.80   $161.80   $161.80  
  Purchase #7 $60.32   9.789%   $66.2247   $66.22   $66.20   $66.20  
  7 purchase totals = $948.98       $1,021.9553   $1,021.96   $1,021.90   $1,022.00