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 $219.61   12.138%   $246.2663   $246.27   $246.25   $246.30  
  Purchase #2 $43.88   3.243%   $45.303   $45.30   $45.30   $45.30  
  Purchase #3 $187.41   7.169%   $200.8454   $200.85   $200.85   $200.80  
  Purchase #4 $55.49   3.244%   $57.2901   $57.29   $57.30   $57.30  
  Purchase #5 $40.95   12.740%   $46.167   $46.17   $46.15   $46.20  
  Purchase #6 $35.44   12.687%   $39.9363   $39.94   $39.95   $39.90  
  Purchase #7 $243.91   10.760%   $270.1547   $270.15   $270.15   $270.20  
  7 purchase totals = $826.69       $905.9628   $905.97   $905.95   $906.00