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 $209.50   12.607%   $235.9117   $235.91   $235.90   $235.90  
  Purchase #2 $83.83   11.840%   $93.7555   $93.76   $93.75   $93.80  
  Purchase #3 $29.36   4.735%   $30.7502   $30.75   $30.75   $30.80  
  Purchase #4 $204.86   8.751%   $222.7873   $222.79   $222.80   $222.80  
  Purchase #5 $244.44   9.268%   $267.0947   $267.09   $267.10   $267.10  
  Purchase #6 $72.96   5.119%   $76.6948   $76.69   $76.70   $76.70  
  Purchase #7 $122.55   8.546%   $133.0231   $133.02   $133.00   $133.00  
  7 purchase totals = $967.50       $1,060.0173   $1,060.01   $1,060.00   $1,060.10