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 $222.78   8.469%   $241.6472   $241.65   $241.65   $241.60  
  Purchase #2 $55.26   8.529%   $59.9731   $59.97   $59.95   $60.00  
  Purchase #3 $26.49   3.815%   $27.5006   $27.50   $27.50   $27.50  
  Purchase #4 $66.85   6.582%   $71.2501   $71.25   $71.25   $71.30  
  Purchase #5 $234.66   10.223%   $258.6493   $258.65   $258.65   $258.60  
  Purchase #6 $41.43   3.553%   $42.902   $42.90   $42.90   $42.90  
  Purchase #7 $178.58   13.183%   $202.1222   $202.12   $202.10   $202.10  
  7 purchase totals = $826.05       $904.0445   $904.04   $904.00   $904.00