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 $50.68   5.790%   $53.6144   $53.61   $53.60   $53.60  
  Purchase #2 $227.78   12.693%   $256.6921   $256.69   $256.70   $256.70  
  Purchase #3 $191.26   5.377%   $201.5441   $201.54   $201.55   $201.50  
  Purchase #4 $165.84   13.839%   $188.7906   $188.79   $188.80   $188.80  
  Purchase #5 $92.70   7.788%   $99.9195   $99.92   $99.90   $99.90  
  Purchase #6 $99.36   6.860%   $106.1761   $106.18   $106.20   $106.20  
  Purchase #7 $19.29   10.419%   $21.2998   $21.30   $21.30   $21.30  
  7 purchase totals = $846.91       $928.0366   $928.03   $928.05   $928.00