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 $120.32   5.449%   $126.8762   $126.88   $126.90   $126.90  
  Purchase #2 $246.69   5.578%   $260.4504   $260.45   $260.45   $260.50  
  Purchase #3 $55.79   7.715%   $60.0942   $60.09   $60.10   $60.10  
  Purchase #4 $140.41   5.128%   $147.6102   $147.61   $147.60   $147.60  
  Purchase #5 $127.73   13.252%   $144.6568   $144.66   $144.65   $144.70  
  Purchase #6 $201.90   11.525%   $225.169   $225.17   $225.15   $225.20  
  Purchase #7 $64.99   6.463%   $69.1903   $69.19   $69.20   $69.20  
  7 purchase totals = $957.83       $1,034.0471   $1,034.05   $1,034.05   $1,034.20