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 $137.84   5.649%   $145.6266   $145.63   $145.65   $145.60  
  Purchase #2 $241.51   9.187%   $263.6975   $263.70   $263.70   $263.70  
  Purchase #3 $67.38   4.635%   $70.5031   $70.50   $70.50   $70.50  
  Purchase #4 $144.46   3.403%   $149.376   $149.38   $149.40   $149.40  
  Purchase #5 $216.54   13.861%   $246.5546   $246.55   $246.55   $246.60  
  Purchase #6 $119.29   5.190%   $125.4812   $125.48   $125.50   $125.50  
  Purchase #7 $26.40   13.186%   $29.8811   $29.88   $29.90   $29.90  
  7 purchase totals = $953.42       $1,031.1201   $1,031.12   $1,031.20   $1,031.20