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 $10.95   6.584%   $11.6709   $11.67   $11.65   $11.70  
  Purchase #2 $238.64   11.678%   $266.5084   $266.51   $266.50   $266.50  
  Purchase #3 $39.39   11.746%   $44.0167   $44.02   $44.00   $44.00  
  Purchase #4 $24.70   4.708%   $25.8629   $25.86   $25.85   $25.90  
  Purchase #5 $109.54   6.813%   $117.003   $117.00   $117.00   $117.00  
  Purchase #6 $23.60   7.124%   $25.2813   $25.28   $25.30   $25.30  
  Purchase #7 $115.48   5.339%   $121.6455   $121.65   $121.65   $121.60  
  7 purchase totals = $562.30       $611.9887   $611.99   $611.95   $612.00