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 $173.73   5.822%   $183.8446   $183.84   $183.85   $183.80  
  Purchase #2 $23.38   6.107%   $24.8078   $24.81   $24.80   $24.80  
  Purchase #3 $153.97   8.706%   $167.3746   $167.37   $167.35   $167.40  
  Purchase #4 $58.46   7.258%   $62.703   $62.70   $62.70   $62.70  
  Purchase #5 $113.77   3.538%   $117.7952   $117.80   $117.80   $117.80  
  Purchase #6 $192.28   9.227%   $210.0217   $210.02   $210.00   $210.00  
  Purchase #7 $208.95   8.270%   $226.2302   $226.23   $226.25   $226.20  
  7 purchase totals = $924.54       $992.7771   $992.77   $992.75   $992.70