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 $61.95   7.651%   $66.6898   $66.69   $66.70   $66.70  
  Purchase #2 $141.81   8.282%   $153.5547   $153.55   $153.55   $153.60  
  Purchase #3 $101.63   11.687%   $113.5075   $113.51   $113.50   $113.50  
  Purchase #4 $70.46   7.364%   $75.6487   $75.65   $75.65   $75.60  
  Purchase #5 $42.32   12.160%   $47.4661   $47.47   $47.45   $47.50  
  Purchase #6 $63.67   11.837%   $71.2066   $71.21   $71.20   $71.20  
  Purchase #7 $144.49   9.602%   $158.3639   $158.36   $158.35   $158.40  
  7 purchase totals = $626.33       $686.4373   $686.44   $686.40   $686.50