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 $95.89   10.638%   $106.0908   $106.09   $106.10   $106.10  
  Purchase #2 $169.29   3.750%   $175.6384   $175.64   $175.65   $175.60  
  Purchase #3 $248.65   6.862%   $265.7124   $265.71   $265.70   $265.70  
  Purchase #4 $118.86   3.547%   $123.076   $123.08   $123.10   $123.10  
  Purchase #5 $68.67   4.226%   $71.572   $71.57   $71.55   $71.60  
  Purchase #6 $9.83   4.775%   $10.2994   $10.30   $10.30   $10.30  
  Purchase #7 $20.26   6.312%   $21.5388   $21.54   $21.55   $21.50  
  7 purchase totals = $731.45       $773.9278   $773.93   $773.95   $773.90