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 $84.92   8.330%   $91.9938   $91.99   $92.00   $92.00  
  Purchase #2 $177.70   7.620%   $191.2407   $191.24   $191.25   $191.20  
  Purchase #3 $15.61   8.302%   $16.9059   $16.91   $16.90   $16.90  
  Purchase #4 $147.59   13.312%   $167.2372   $167.24   $167.25   $167.20  
  Purchase #5 $63.88   6.592%   $68.091   $68.09   $68.10   $68.10  
  Purchase #6 $14.87   5.257%   $15.6517   $15.65   $15.65   $15.70  
  Purchase #7 $10.36   12.647%   $11.6702   $11.67   $11.65   $11.70  
  7 purchase totals = $514.93       $562.7905   $562.79   $562.80   $562.80