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 $144.44   13.674%   $164.1907   $164.19   $164.20   $164.20  
  Purchase #2 $201.28   11.641%   $224.711   $224.71   $224.70   $224.70  
  Purchase #3 $57.66   9.850%   $63.3395   $63.34   $63.35   $63.30  
  Purchase #4 $168.83   7.203%   $180.9908   $180.99   $181.00   $181.00  
  Purchase #5 $243.46   13.598%   $276.5657   $276.57   $276.55   $276.60  
  Purchase #6 $95.30   5.402%   $100.4481   $100.45   $100.45   $100.40  
  Purchase #7 $58.25   9.849%   $63.987   $63.99   $64.00   $64.00  
  7 purchase totals = $969.22       $1,074.2328   $1,074.24   $1,074.25   $1,074.20