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 $58.76   5.276%   $61.8602   $61.86   $61.85   $61.90  
  Purchase #2 $14.70   7.346%   $15.7799   $15.78   $15.80   $15.80  
  Purchase #3 $60.54   10.695%   $67.0148   $67.01   $67.00   $67.00  
  Purchase #4 $185.68   9.579%   $203.4663   $203.47   $203.45   $203.50  
  Purchase #5 $192.74   13.301%   $218.3763   $218.38   $218.40   $218.40  
  Purchase #6 $149.80   6.840%   $160.0463   $160.05   $160.05   $160.00  
  Purchase #7 $236.29   5.399%   $249.0473   $249.05   $249.05   $249.00  
  7 purchase totals = $898.51       $975.5911   $975.60   $975.60   $975.60