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 $61.36   4.577%   $64.1684   $64.17   $64.15   $64.20  
  Purchase #2 $167.88   4.452%   $175.354   $175.35   $175.35   $175.40  
  Purchase #3 $59.38   12.191%   $66.619   $66.62   $66.60   $66.60  
  Purchase #4 $244.57   10.772%   $270.9151   $270.92   $270.90   $270.90  
  Purchase #5 $32.42   4.337%   $33.8261   $33.83   $33.85   $33.80  
  Purchase #6 $156.69   13.445%   $177.757   $177.76   $177.75   $177.80  
  Purchase #7 $49.87   13.675%   $56.6897   $56.69   $56.70   $56.70  
  7 purchase totals = $772.17       $845.3293   $845.34   $845.30   $845.40