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 $208.36   13.220%   $235.9052   $235.91   $235.90   $235.90  
  Purchase #2 $137.97   10.842%   $152.9287   $152.93   $152.95   $152.90  
  Purchase #3 $63.98   7.543%   $68.806   $68.81   $68.80   $68.80  
  Purchase #4 $183.50   4.272%   $191.3391   $191.34   $191.35   $191.30  
  Purchase #5 $133.95   7.287%   $143.7109   $143.71   $143.70   $143.70  
  Purchase #6 $45.85   5.446%   $48.347   $48.35   $48.35   $48.30  
  Purchase #7 $18.47   9.743%   $20.2695   $20.27   $20.25   $20.30  
  7 purchase totals = $792.08       $861.3064   $861.32   $861.30   $861.20