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 $57.76   7.362%   $62.0123   $62.01   $62.00   $62.00  
  Purchase #2 $171.42   5.383%   $180.6475   $180.65   $180.65   $180.60  
  Purchase #3 $178.70   7.126%   $191.4342   $191.43   $191.45   $191.40  
  Purchase #4 $7.33   6.789%   $7.8276   $7.83   $7.85   $7.80  
  Purchase #5 $147.44   10.467%   $162.8725   $162.87   $162.85   $162.90  
  Purchase #6 $47.87   5.126%   $50.3238   $50.32   $50.30   $50.30  
  Purchase #7 $186.85   10.238%   $205.9797   $205.98   $206.00   $206.00  
  7 purchase totals = $797.37       $861.0976   $861.09   $861.10   $861.00