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 $67.71   10.608%   $74.8927   $74.89   $74.90   $74.90  
  Purchase #2 $39.55   4.346%   $41.2688   $41.27   $41.25   $41.30  
  Purchase #3 $40.85   6.551%   $43.5261   $43.53   $43.55   $43.50  
  Purchase #4 $193.41   13.598%   $219.7099   $219.71   $219.70   $219.70  
  Purchase #5 $177.30   5.411%   $186.8937   $186.89   $186.90   $186.90  
  Purchase #6 $181.64   12.510%   $204.3632   $204.36   $204.35   $204.40  
  Purchase #7 $226.45   9.513%   $247.9922   $247.99   $248.00   $248.00  
  7 purchase totals = $926.91       $1,018.6466   $1,018.64   $1,018.65   $1,018.70