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 $241.93   8.458%   $262.3924   $262.39   $262.40   $262.40  
  Purchase #2 $77.81   12.838%   $87.7992   $87.80   $87.80   $87.80  
  Purchase #3 $224.72   13.355%   $254.7314   $254.73   $254.75   $254.70  
  Purchase #4 $52.37   9.542%   $57.3671   $57.37   $57.35   $57.40  
  Purchase #5 $241.62   5.319%   $254.4718   $254.47   $254.45   $254.50  
  Purchase #6 $209.37   8.384%   $226.9236   $226.92   $226.90   $226.90  
  Purchase #7 $200.68   9.402%   $219.5479   $219.55   $219.55   $219.50  
  7 purchase totals = $1,248.50       $1,363.2334   $1,363.23   $1,363.20   $1,363.20