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 $89.45   5.702%   $94.5504   $94.55   $94.55   $94.60  
  Purchase #2 $209.55   4.591%   $219.1704   $219.17   $219.15   $219.20  
  Purchase #3 $83.49   4.832%   $87.5242   $87.52   $87.50   $87.50  
  Purchase #4 $200.87   13.468%   $227.9232   $227.92   $227.90   $227.90  
  Purchase #5 $156.35   4.795%   $163.847   $163.85   $163.85   $163.80  
  Purchase #6 $219.97   5.545%   $232.1673   $232.17   $232.15   $232.20  
  Purchase #7 $203.57   5.463%   $214.691   $214.69   $214.70   $214.70  
  7 purchase totals = $1,163.25       $1,239.8735   $1,239.87   $1,239.80   $1,239.90