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 $245.54   9.773%   $269.5366   $269.54   $269.55   $269.50  
  Purchase #2 $111.92   12.248%   $125.628   $125.63   $125.65   $125.60  
  Purchase #3 $161.76   5.609%   $170.8331   $170.83   $170.85   $170.80  
  Purchase #4 $56.46   11.722%   $63.0782   $63.08   $63.10   $63.10  
  Purchase #5 $220.84   12.278%   $247.9547   $247.95   $247.95   $248.00  
  Purchase #6 $192.52   9.775%   $211.3388   $211.34   $211.35   $211.30  
  Purchase #7 $122.91   4.544%   $128.495   $128.50   $128.50   $128.50  
  7 purchase totals = $1,111.95       $1,216.8644   $1,216.87   $1,216.95   $1,216.80