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 $50.39   6.521%   $53.6759   $53.68   $53.70   $53.70  
  Purchase #2 $209.63   3.770%   $217.5331   $217.53   $217.55   $217.50  
  Purchase #3 $71.67   6.254%   $76.1522   $76.15   $76.15   $76.20  
  Purchase #4 $50.62   3.651%   $52.4681   $52.47   $52.45   $52.50  
  Purchase #5 $177.80   13.657%   $202.0821   $202.08   $202.10   $202.10  
  Purchase #6 $119.37   4.465%   $124.6999   $124.70   $124.70   $124.70  
  Purchase #7 $250.64   13.354%   $284.1105   $284.11   $284.10   $284.10  
  7 purchase totals = $930.12       $1,010.7218   $1,010.72   $1,010.75   $1,010.80