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 $53.94   11.137%   $59.9473   $59.95   $59.95   $59.90  
  Purchase #2 $245.76   3.248%   $253.7423   $253.74   $253.75   $253.70  
  Purchase #3 $223.28   12.861%   $251.996   $252.00   $252.00   $252.00  
  Purchase #4 $22.80   6.379%   $24.2544   $24.25   $24.25   $24.30  
  Purchase #5 $205.93   3.756%   $213.6647   $213.66   $213.65   $213.70  
  Purchase #6 $176.95   5.725%   $187.0804   $187.08   $187.10   $187.10  
  Purchase #7 $133.47   10.384%   $147.3295   $147.33   $147.35   $147.30  
  7 purchase totals = $1,062.13       $1,138.0146   $1,138.01   $1,138.05   $1,138.00