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 $23.61   8.628%   $25.6471   $25.65   $25.65   $25.60  
  Purchase #2 $47.96   3.533%   $49.6544   $49.65   $49.65   $49.70  
  Purchase #3 $229.87   10.447%   $253.8845   $253.88   $253.90   $253.90  
  Purchase #4 $224.95   3.431%   $232.668   $232.67   $232.65   $232.70  
  Purchase #5 $182.74   7.156%   $195.8169   $195.82   $195.80   $195.80  
  Purchase #6 $189.86   8.479%   $205.9582   $205.96   $205.95   $206.00  
  Purchase #7 $51.54   8.625%   $55.9853   $55.99   $56.00   $56.00  
  7 purchase totals = $950.53       $1,019.6144   $1,019.62   $1,019.60   $1,019.70