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 $245.98   9.402%   $269.107   $269.11   $269.10   $269.10  
  Purchase #2 $144.52   8.403%   $156.664   $156.66   $156.65   $156.70  
  Purchase #3 $209.41   3.537%   $216.8168   $216.82   $216.80   $216.80  
  Purchase #4 $42.52   7.277%   $45.6142   $45.61   $45.60   $45.60  
  Purchase #5 $123.40   8.469%   $133.8507   $133.85   $133.85   $133.90  
  Purchase #6 $21.94   6.179%   $23.2957   $23.30   $23.30   $23.30  
  Purchase #7 $196.53   6.181%   $208.6775   $208.68   $208.70   $208.70  
  7 purchase totals = $984.30       $1,054.0259   $1,054.03   $1,054.00   $1,054.10