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 $241.65   8.665%   $262.589   $262.59   $262.60   $262.60  
  Purchase #2 $37.90   3.850%   $39.3592   $39.36   $39.35   $39.40  
  Purchase #3 $46.87   12.220%   $52.5975   $52.60   $52.60   $52.60  
  Purchase #4 $51.86   3.160%   $53.4988   $53.50   $53.50   $53.50  
  Purchase #5 $235.54   4.409%   $245.925   $245.93   $245.95   $245.90  
  Purchase #6 $167.98   4.347%   $175.2821   $175.28   $175.30   $175.30  
  Purchase #7 $59.49   6.730%   $63.4937   $63.49   $63.50   $63.50  
  7 purchase totals = $841.29       $892.7453   $892.75   $892.80   $892.80