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 $129.59   3.605%   $134.2617   $134.26   $134.25   $134.30  
  Purchase #2 $205.81   12.210%   $230.9394   $230.94   $230.95   $230.90  
  Purchase #3 $240.72   7.538%   $258.8655   $258.87   $258.85   $258.90  
  Purchase #4 $22.70   9.608%   $24.881   $24.88   $24.90   $24.90  
  Purchase #5 $199.95   6.244%   $212.4349   $212.43   $212.45   $212.40  
  Purchase #6 $118.95   3.423%   $123.0217   $123.02   $123.00   $123.00  
  Purchase #7 $43.65   5.486%   $46.0446   $46.04   $46.05   $46.00  
  7 purchase totals = $961.37       $1,030.4488   $1,030.44   $1,030.45   $1,030.40