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 $156.26   7.414%   $167.8451   $167.85   $167.85   $167.80  
  Purchase #2 $101.86   4.613%   $106.5588   $106.56   $106.55   $106.60  
  Purchase #3 $200.89   4.393%   $209.7151   $209.72   $209.70   $209.70  
  Purchase #4 $130.26   5.401%   $137.2953   $137.30   $137.30   $137.30  
  Purchase #5 $161.94   3.605%   $167.7779   $167.78   $167.80   $167.80  
  Purchase #6 $167.74   12.282%   $188.3418   $188.34   $188.35   $188.30  
  Purchase #7 $69.26   10.116%   $76.2663   $76.27   $76.25   $76.30  
  7 purchase totals = $988.21       $1,053.8003   $1,053.82   $1,053.80   $1,053.80