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 $68.49   12.103%   $76.7793   $76.78   $76.80   $76.80  
  Purchase #2 $147.49   9.338%   $161.2626   $161.26   $161.25   $161.30  
  Purchase #3 $183.69   10.179%   $202.3878   $202.39   $202.40   $202.40  
  Purchase #4 $136.97   10.183%   $150.9177   $150.92   $150.90   $150.90  
  Purchase #5 $79.50   13.160%   $89.9622   $89.96   $89.95   $90.00  
  Purchase #6 $89.77   12.548%   $101.0343   $101.03   $101.05   $101.00  
  Purchase #7 $46.57   8.816%   $50.6756   $50.68   $50.70   $50.70  
  7 purchase totals = $752.48       $833.0195   $833.02   $833.05   $833.10