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 $164.97   11.523%   $183.9795   $183.98   $184.00   $184.00  
  Purchase #2 $96.51   3.683%   $100.0645   $100.06   $100.05   $100.10  
  Purchase #3 $32.26   3.381%   $33.3507   $33.35   $33.35   $33.40  
  Purchase #4 $49.46   9.142%   $53.9816   $53.98   $54.00   $54.00  
  Purchase #5 $248.87   9.500%   $272.5127   $272.51   $272.50   $272.50  
  Purchase #6 $21.38   11.113%   $23.756   $23.76   $23.75   $23.80  
  Purchase #7 $227.42   13.301%   $257.6691   $257.67   $257.65   $257.70  
  7 purchase totals = $840.87       $925.3141   $925.31   $925.30   $925.50