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 $214.54   13.356%   $243.194   $243.19   $243.20   $243.20  
  Purchase #2 $127.51   7.797%   $137.452   $137.45   $137.45   $137.50  
  Purchase #3 $151.73   3.111%   $156.4503   $156.45   $156.45   $156.50  
  Purchase #4 $63.69   11.569%   $71.0583   $71.06   $71.05   $71.10  
  Purchase #5 $68.38   7.282%   $73.3594   $73.36   $73.35   $73.40  
  Purchase #6 $244.74   6.109%   $259.6912   $259.69   $259.70   $259.70  
  Purchase #7 $247.28   10.352%   $272.8784   $272.88   $272.90   $272.90  
  7 purchase totals = $1,117.87       $1,214.0836   $1,214.08   $1,214.10   $1,214.30