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 $71.70   4.148%   $74.6741   $74.67   $74.65   $74.70  
  Purchase #2 $222.64   11.752%   $248.8047   $248.80   $248.80   $248.80  
  Purchase #3 $85.93   7.785%   $92.6197   $92.62   $92.60   $92.60  
  Purchase #4 $84.36   6.669%   $89.986   $89.99   $90.00   $90.00  
  Purchase #5 $39.86   10.114%   $43.8914   $43.89   $43.90   $43.90  
  Purchase #6 $214.69   10.840%   $237.9624   $237.96   $237.95   $238.00  
  Purchase #7 $12.87   5.338%   $13.557   $13.56   $13.55   $13.60  
  7 purchase totals = $732.05       $801.4953   $801.49   $801.45   $801.60