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 $30.42   7.393%   $32.669   $32.67   $32.65   $32.70  
  Purchase #2 $85.39   11.805%   $95.4703   $95.47   $95.45   $95.50  
  Purchase #3 $219.48   9.816%   $241.0242   $241.02   $241.00   $241.00  
  Purchase #4 $31.64   4.469%   $33.054   $33.05   $33.05   $33.10  
  Purchase #5 $115.92   3.449%   $119.9181   $119.92   $119.90   $119.90  
  Purchase #6 $170.85   7.813%   $184.1985   $184.20   $184.20   $184.20  
  Purchase #7 $194.91   11.807%   $217.923   $217.92   $217.90   $217.90  
  7 purchase totals = $848.61       $924.2571   $924.25   $924.15   $924.30