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 $219.49   12.197%   $246.2612   $246.26   $246.25   $246.30  
  Purchase #2 $111.40   10.865%   $123.5036   $123.50   $123.50   $123.50  
  Purchase #3 $65.60   7.757%   $70.6886   $70.69   $70.70   $70.70  
  Purchase #4 $64.36   9.246%   $70.3107   $70.31   $70.30   $70.30  
  Purchase #5 $233.59   8.164%   $252.6603   $252.66   $252.65   $252.70  
  Purchase #6 $100.74   7.172%   $107.9651   $107.97   $107.95   $108.00  
  Purchase #7 $193.91   4.386%   $202.4149   $202.41   $202.40   $202.40  
  7 purchase totals = $989.09       $1,073.8044   $1,073.80   $1,073.75   $1,073.90