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 $186.69   13.550%   $211.9865   $211.99   $212.00   $212.00  
  Purchase #2 $10.65   9.802%   $11.6939   $11.69   $11.70   $11.70  
  Purchase #3 $31.63   4.293%   $32.9879   $32.99   $33.00   $33.00  
  Purchase #4 $48.75   9.275%   $53.2716   $53.27   $53.25   $53.30  
  Purchase #5 $120.40   12.178%   $135.0623   $135.06   $135.05   $135.10  
  Purchase #6 $10.33   5.378%   $10.8855   $10.89   $10.90   $10.90  
  Purchase #7 $9.79   10.396%   $10.8078   $10.81   $10.80   $10.80  
  7 purchase totals = $418.24       $466.6955   $466.70   $466.70   $466.80