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 $92.49   7.636%   $99.5525   $99.55   $99.55   $99.60  
  Purchase #2 $214.88   6.727%   $229.335   $229.34   $229.35   $229.30  
  Purchase #3 $54.49   3.217%   $56.2429   $56.24   $56.25   $56.20  
  Purchase #4 $67.67   10.452%   $74.7429   $74.74   $74.75   $74.70  
  Purchase #5 $187.77   9.688%   $205.9612   $205.96   $205.95   $206.00  
  Purchase #6 $191.46   3.557%   $198.2702   $198.27   $198.25   $198.30  
  Purchase #7 $159.32   11.408%   $177.4952   $177.50   $177.50   $177.50  
  7 purchase totals = $968.08       $1,041.5999   $1,041.60   $1,041.60   $1,041.60