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 $154.25   7.335%   $165.5642   $165.56   $165.55   $165.60  
  Purchase #2 $16.38   11.721%   $18.2999   $18.30   $18.30   $18.30  
  Purchase #3 $203.75   4.606%   $213.1347   $213.13   $213.15   $213.10  
  Purchase #4 $205.96   11.769%   $230.1994   $230.20   $230.20   $230.20  
  Purchase #5 $235.34   12.776%   $265.407   $265.41   $265.40   $265.40  
  Purchase #6 $15.25   3.659%   $15.808   $15.81   $15.80   $15.80  
  Purchase #7 $58.51   8.524%   $63.4974   $63.50   $63.50   $63.50  
  7 purchase totals = $889.44       $971.9106   $971.91   $971.90   $971.90