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 $241.82   12.794%   $272.7585   $272.76   $272.75   $272.80  
  Purchase #2 $135.65   3.792%   $140.7938   $140.79   $140.80   $140.80  
  Purchase #3 $189.28   9.559%   $207.3733   $207.37   $207.35   $207.40  
  Purchase #4 $19.99   10.451%   $22.0792   $22.08   $22.10   $22.10  
  Purchase #5 $22.83   4.357%   $23.8247   $23.82   $23.80   $23.80  
  Purchase #6 $193.78   4.195%   $201.9091   $201.91   $201.90   $201.90  
  Purchase #7 $131.39   10.800%   $145.5801   $145.58   $145.60   $145.60  
  7 purchase totals = $934.74       $1,014.3187   $1,014.31   $1,014.30   $1,014.40