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 $55.49   12.233%   $62.2781   $62.28   $62.30   $62.30  
  Purchase #2 $177.73   6.242%   $188.8239   $188.82   $188.80   $188.80  
  Purchase #3 $47.60   3.495%   $49.2636   $49.26   $49.25   $49.30  
  Purchase #4 $230.31   8.535%   $249.967   $249.97   $249.95   $250.00  
  Purchase #5 $162.40   8.456%   $176.1325   $176.13   $176.15   $176.10  
  Purchase #6 $164.66   10.517%   $181.9773   $181.98   $182.00   $182.00  
  Purchase #7 $95.86   12.749%   $108.0812   $108.08   $108.10   $108.10  
  7 purchase totals = $934.05       $1,016.5236   $1,016.52   $1,016.55   $1,016.60