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 $33.38   11.645%   $37.2671   $37.27   $37.25   $37.30  
  Purchase #2 $54.43   13.523%   $61.7906   $61.79   $61.80   $61.80  
  Purchase #3 $232.66   8.492%   $252.4175   $252.42   $252.40   $252.40  
  Purchase #4 $152.41   9.105%   $166.2869   $166.29   $166.30   $166.30  
  Purchase #5 $91.77   3.534%   $95.0132   $95.01   $95.00   $95.00  
  Purchase #6 $135.68   3.431%   $140.3352   $140.34   $140.35   $140.30  
  Purchase #7 $236.82   9.190%   $258.5838   $258.58   $258.60   $258.60  
  7 purchase totals = $937.15       $1,011.6943   $1,011.70   $1,011.70   $1,011.70