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 $68.26   11.497%   $76.1079   $76.11   $76.10   $76.10  
  Purchase #2 $116.82   6.521%   $124.4378   $124.44   $124.45   $124.40  
  Purchase #3 $89.76   7.166%   $96.1922   $96.19   $96.20   $96.20  
  Purchase #4 $134.80   11.241%   $149.9529   $149.95   $149.95   $150.00  
  Purchase #5 $55.62   3.160%   $57.3776   $57.38   $57.40   $57.40  
  Purchase #6 $22.55   4.837%   $23.6407   $23.64   $23.65   $23.60  
  Purchase #7 $6.89   3.693%   $7.1444   $7.14   $7.15   $7.10  
  7 purchase totals = $494.70       $534.8535   $534.85   $534.90   $534.80