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 $61.42   13.385%   $69.6411   $69.64   $69.65   $69.60  
  Purchase #2 $92.61   11.633%   $103.3833   $103.38   $103.40   $103.40  
  Purchase #3 $209.56   3.702%   $217.3179   $217.32   $217.30   $217.30  
  Purchase #4 $102.37   3.363%   $105.8127   $105.81   $105.80   $105.80  
  Purchase #5 $223.84   10.235%   $246.75   $246.75   $246.75   $246.80  
  Purchase #6 $190.92   5.446%   $201.3175   $201.32   $201.30   $201.30  
  Purchase #7 $52.86   4.582%   $55.282   $55.28   $55.30   $55.30  
  7 purchase totals = $933.58       $999.5045   $999.50   $999.50   $999.50