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 $224.43   7.467%   $241.1882   $241.19   $241.20   $241.20  
  Purchase #2 $51.81   3.860%   $53.8099   $53.81   $53.80   $53.80  
  Purchase #3 $78.72   5.724%   $83.2259   $83.23   $83.25   $83.20  
  Purchase #4 $169.87   11.413%   $189.2573   $189.26   $189.25   $189.30  
  Purchase #5 $71.66   12.312%   $80.4828   $80.48   $80.50   $80.50  
  Purchase #6 $164.75   13.389%   $186.8084   $186.81   $186.80   $186.80  
  Purchase #7 $124.93   6.623%   $133.2041   $133.20   $133.20   $133.20  
  7 purchase totals = $886.17       $967.9766   $967.98   $968.00   $968.00