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 $131.46   7.770%   $141.6744   $141.67   $141.65   $141.70  
  Purchase #2 $27.29   11.634%   $30.4649   $30.46   $30.45   $30.50  
  Purchase #3 $51.76   4.816%   $54.2528   $54.25   $54.25   $54.30  
  Purchase #4 $218.84   13.695%   $248.8101   $248.81   $248.80   $248.80  
  Purchase #5 $35.96   4.682%   $37.6436   $37.64   $37.65   $37.60  
  Purchase #6 $184.40   13.470%   $209.2387   $209.24   $209.25   $209.20  
  Purchase #7 $168.34   4.319%   $175.6106   $175.61   $175.60   $175.60  
  7 purchase totals = $818.05       $897.6951   $897.68   $897.65   $897.70