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 $234.81   8.512%   $254.797   $254.80   $254.80   $254.80  
  Purchase #2 $137.65   5.341%   $145.0019   $145.00   $145.00   $145.00  
  Purchase #3 $114.96   10.793%   $127.3676   $127.37   $127.35   $127.40  
  Purchase #4 $92.63   5.155%   $97.4051   $97.41   $97.40   $97.40  
  Purchase #5 $224.92   12.741%   $253.5771   $253.58   $253.60   $253.60  
  Purchase #6 $107.40   3.747%   $111.4243   $111.42   $111.40   $111.40  
  Purchase #7 $56.61   6.367%   $60.2144   $60.21   $60.20   $60.20  
  7 purchase totals = $968.98       $1,049.7874   $1,049.79   $1,049.75   $1,049.80