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 $56.61   3.661%   $58.6825   $58.68   $58.70   $58.70  
  Purchase #2 $237.91   10.468%   $262.8144   $262.81   $262.80   $262.80  
  Purchase #3 $83.62   7.171%   $89.6164   $89.62   $89.60   $89.60  
  Purchase #4 $82.91   11.649%   $92.5682   $92.57   $92.55   $92.60  
  Purchase #5 $7.60   7.257%   $8.1515   $8.15   $8.15   $8.20  
  Purchase #6 $239.45   11.122%   $266.0816   $266.08   $266.10   $266.10  
  Purchase #7 $64.47   5.529%   $68.0345   $68.03   $68.05   $68.00  
  7 purchase totals = $772.57       $845.9491   $845.94   $845.95   $846.00