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 $54.36   12.321%   $61.0577   $61.06   $61.05   $61.10  
  Purchase #2 $61.72   6.866%   $65.9577   $65.96   $65.95   $66.00  
  Purchase #3 $171.28   12.124%   $192.046   $192.05   $192.05   $192.00  
  Purchase #4 $17.64   8.695%   $19.1738   $19.17   $19.15   $19.20  
  Purchase #5 $207.83   10.757%   $230.1863   $230.19   $230.20   $230.20  
  Purchase #6 $67.26   8.300%   $72.8426   $72.84   $72.85   $72.80  
  Purchase #7 $194.59   4.275%   $202.9087   $202.91   $202.90   $202.90  
  7 purchase totals = $774.68       $844.1728   $844.18   $844.15   $844.20