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 $245.49   9.721%   $269.3541   $269.35   $269.35   $269.40  
  Purchase #2 $138.65   4.198%   $144.4705   $144.47   $144.45   $144.50  
  Purchase #3 $59.69   3.405%   $61.7224   $61.72   $61.70   $61.70  
  Purchase #4 $231.30   11.455%   $257.7954   $257.80   $257.80   $257.80  
  Purchase #5 $157.83   5.454%   $166.438   $166.44   $166.45   $166.40  
  Purchase #6 $161.53   3.784%   $167.6423   $167.64   $167.65   $167.60  
  Purchase #7 $178.57   10.523%   $197.3609   $197.36   $197.35   $197.40  
  7 purchase totals = $1,173.06       $1,264.7836   $1,264.78   $1,264.75   $1,264.80