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 $65.29   12.616%   $73.527   $73.53   $73.55   $73.50  
  Purchase #2 $136.78   3.207%   $141.1665   $141.17   $141.15   $141.20  
  Purchase #3 $53.62   4.495%   $56.0302   $56.03   $56.05   $56.00  
  Purchase #4 $6.53   6.138%   $6.9308   $6.93   $6.95   $6.90  
  Purchase #5 $170.91   6.359%   $181.7782   $181.78   $181.80   $181.80  
  Purchase #6 $240.56   3.819%   $249.747   $249.75   $249.75   $249.70  
  Purchase #7 $182.45   12.627%   $205.488   $205.49   $205.50   $205.50  
  7 purchase totals = $856.14       $914.6677   $914.68   $914.75   $914.60