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 $14.54   11.368%   $16.1929   $16.19   $16.20   $16.20  
  Purchase #2 $235.85   8.178%   $255.1378   $255.14   $255.15   $255.10  
  Purchase #3 $211.32   6.819%   $225.7299   $225.73   $225.75   $225.70  
  Purchase #4 $31.74   8.144%   $34.3249   $34.32   $34.30   $34.30  
  Purchase #5 $33.78   5.420%   $35.6109   $35.61   $35.60   $35.60  
  Purchase #6 $147.35   11.663%   $164.5354   $164.54   $164.55   $164.50  
  Purchase #7 $247.46   7.825%   $266.8237   $266.82   $266.80   $266.80  
  7 purchase totals = $922.04       $998.3555   $998.35   $998.35   $998.20