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 $61.73   13.623%   $70.1395   $70.14   $70.15   $70.10  
  Purchase #2 $69.64   5.292%   $73.3253   $73.33   $73.35   $73.30  
  Purchase #3 $229.26   7.661%   $246.8236   $246.82   $246.80   $246.80  
  Purchase #4 $80.99   13.240%   $91.7131   $91.71   $91.70   $91.70  
  Purchase #5 $120.33   12.504%   $135.3761   $135.38   $135.40   $135.40  
  Purchase #6 $199.49   3.795%   $207.0606   $207.06   $207.05   $207.10  
  Purchase #7 $53.92   8.562%   $58.5366   $58.54   $58.55   $58.50  
  7 purchase totals = $815.36       $882.9748   $882.98   $883.00   $882.90