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 $67.58   12.426%   $75.9775   $75.98   $76.00   $76.00  
  Purchase #2 $225.96   12.567%   $254.3564   $254.36   $254.35   $254.40  
  Purchase #3 $159.68   10.730%   $176.8137   $176.81   $176.80   $176.80  
  Purchase #4 $106.65   7.782%   $114.9495   $114.95   $114.95   $114.90  
  Purchase #5 $105.63   3.694%   $109.532   $109.53   $109.55   $109.50  
  Purchase #6 $11.26   6.769%   $12.0222   $12.02   $12.00   $12.00  
  Purchase #7 $41.96   5.192%   $44.1386   $44.14   $44.15   $44.10  
  7 purchase totals = $718.72       $787.7899   $787.79   $787.80   $787.70