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 $89.74   13.124%   $101.5175   $101.52   $101.50   $101.50  
  Purchase #2 $195.91   13.441%   $222.2423   $222.24   $222.25   $222.20  
  Purchase #3 $114.71   3.496%   $118.7203   $118.72   $118.70   $118.70  
  Purchase #4 $155.26   13.858%   $176.7759   $176.78   $176.80   $176.80  
  Purchase #5 $175.64   10.198%   $193.5518   $193.55   $193.55   $193.60  
  Purchase #6 $213.87   7.841%   $230.6395   $230.64   $230.65   $230.60  
  Purchase #7 $58.91   9.689%   $64.6178   $64.62   $64.60   $64.60  
  7 purchase totals = $1,004.04       $1,108.0651   $1,108.07   $1,108.05   $1,108.00