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 $37.87   10.671%   $41.9111   $41.91   $41.90   $41.90  
  Purchase #2 $87.80   8.200%   $94.9996   $95.00   $95.00   $95.00  
  Purchase #3 $195.28   7.646%   $210.2111   $210.21   $210.20   $210.20  
  Purchase #4 $14.93   10.208%   $16.4541   $16.45   $16.45   $16.50  
  Purchase #5 $190.48   5.784%   $201.4974   $201.50   $201.50   $201.50  
  Purchase #6 $244.34   10.389%   $269.7245   $269.72   $269.70   $269.70  
  Purchase #7 $196.51   13.308%   $222.6616   $222.66   $222.65   $222.70  
  7 purchase totals = $967.21       $1,057.4594   $1,057.45   $1,057.40   $1,057.50