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 $5.42   4.553%   $5.6668   $5.67   $5.65   $5.70  
  Purchase #2 $5.90   7.547%   $6.3453   $6.35   $6.35   $6.30  
  Purchase #3 $37.64   7.208%   $40.3531   $40.35   $40.35   $40.40  
  Purchase #4 $230.66   12.705%   $259.9654   $259.97   $259.95   $260.00  
  Purchase #5 $117.32   5.315%   $123.5556   $123.56   $123.55   $123.60  
  Purchase #6 $34.81   7.800%   $37.5252   $37.53   $37.55   $37.50  
  Purchase #7 $111.40   9.775%   $122.2894   $122.29   $122.30   $122.30  
  7 purchase totals = $543.15       $595.7008   $595.72   $595.70   $595.80