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 $59.75   6.571%   $63.6762   $63.68   $63.70   $63.70  
  Purchase #2 $132.70   7.436%   $142.5676   $142.57   $142.55   $142.60  
  Purchase #3 $76.89   9.530%   $84.2176   $84.22   $84.20   $84.20  
  Purchase #4 $167.85   12.298%   $188.4922   $188.49   $188.50   $188.50  
  Purchase #5 $125.60   9.864%   $137.9892   $137.99   $138.00   $138.00  
  Purchase #6 $104.76   12.325%   $117.6717   $117.67   $117.65   $117.70  
  Purchase #7 $109.33   13.662%   $124.2667   $124.27   $124.25   $124.30  
  7 purchase totals = $776.88       $858.8812   $858.89   $858.85   $859.00