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 $58.91   13.459%   $66.8387   $66.84   $66.85   $66.80  
  Purchase #2 $64.33   6.417%   $68.4581   $68.46   $68.45   $68.50  
  Purchase #3 $242.70   10.704%   $268.6786   $268.68   $268.70   $268.70  
  Purchase #4 $93.68   12.278%   $105.182   $105.18   $105.20   $105.20  
  Purchase #5 $64.68   8.556%   $70.214   $70.21   $70.20   $70.20  
  Purchase #6 $200.95   6.220%   $213.4491   $213.45   $213.45   $213.40  
  Purchase #7 $95.70   3.718%   $99.2581   $99.26   $99.25   $99.30  
  7 purchase totals = $820.95       $892.0786   $892.08   $892.10   $892.10