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 $60.59   10.595%   $67.0095   $67.01   $67.00   $67.00  
  Purchase #2 $173.75   8.751%   $188.9549   $188.95   $188.95   $189.00  
  Purchase #3 $137.62   6.734%   $146.8873   $146.89   $146.90   $146.90  
  Purchase #4 $132.78   11.814%   $148.4666   $148.47   $148.45   $148.50  
  Purchase #5 $188.30   7.640%   $202.6861   $202.69   $202.70   $202.70  
  Purchase #6 $68.51   10.636%   $75.7967   $75.80   $75.80   $75.80  
  Purchase #7 $219.58   8.365%   $237.9479   $237.95   $237.95   $237.90  
  7 purchase totals = $981.13       $1,067.7490   $1,067.76   $1,067.75   $1,067.80