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 $239.84   5.471%   $252.9616   $252.96   $252.95   $253.00  
  Purchase #2 $56.78   5.630%   $59.9767   $59.98   $60.00   $60.00  
  Purchase #3 $250.85   13.198%   $283.9572   $283.96   $283.95   $284.00  
  Purchase #4 $250.35   4.874%   $262.5521   $262.55   $262.55   $262.60  
  Purchase #5 $186.98   6.148%   $198.4755   $198.48   $198.50   $198.50  
  Purchase #6 $106.63   5.220%   $112.1961   $112.20   $112.20   $112.20  
  Purchase #7 $149.95   5.701%   $158.4986   $158.50   $158.50   $158.50  
  7 purchase totals = $1,241.38       $1,328.6178   $1,328.63   $1,328.65   $1,328.80