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 $95.63   12.154%   $107.2529   $107.25   $107.25   $107.30  
  Purchase #2 $223.41   12.613%   $251.5887   $251.59   $251.60   $251.60  
  Purchase #3 $106.48   6.867%   $113.792   $113.79   $113.80   $113.80  
  Purchase #4 $73.38   7.278%   $78.7206   $78.72   $78.70   $78.70  
  Purchase #5 $250.78   7.306%   $269.102   $269.10   $269.10   $269.10  
  Purchase #6 $193.65   10.165%   $213.3345   $213.33   $213.35   $213.30  
  Purchase #7 $33.35   7.750%   $35.9346   $35.93   $35.95   $35.90  
  7 purchase totals = $976.68       $1,069.7253   $1,069.71   $1,069.75   $1,069.70