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 $59.29   10.612%   $65.5819   $65.58   $65.60   $65.60  
  Purchase #2 $151.64   9.263%   $165.6864   $165.69   $165.70   $165.70  
  Purchase #3 $65.97   8.699%   $71.7087   $71.71   $71.70   $71.70  
  Purchase #4 $181.78   8.367%   $196.9895   $196.99   $197.00   $197.00  
  Purchase #5 $5.45   10.461%   $6.0201   $6.02   $6.00   $6.00  
  Purchase #6 $181.70   6.349%   $193.2361   $193.24   $193.25   $193.20  
  Purchase #7 $49.63   4.666%   $51.9457   $51.95   $51.95   $51.90  
  7 purchase totals = $695.46       $751.1684   $751.18   $751.20   $751.10