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 $201.93   11.305%   $224.7582   $224.76   $224.75   $224.80  
  Purchase #2 $53.62   12.273%   $60.2008   $60.20   $60.20   $60.20  
  Purchase #3 $223.48   9.747%   $245.2626   $245.26   $245.25   $245.30  
  Purchase #4 $144.99   11.183%   $161.2042   $161.20   $161.20   $161.20  
  Purchase #5 $81.37   4.355%   $84.9137   $84.91   $84.90   $84.90  
  Purchase #6 $98.77   7.823%   $106.4968   $106.50   $106.50   $106.50  
  Purchase #7 $216.48   7.164%   $231.9886   $231.99   $232.00   $232.00  
  7 purchase totals = $1,020.64       $1,114.8249   $1,114.82   $1,114.80   $1,114.90