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 $37.35   10.479%   $41.2639   $41.26   $41.25   $41.30  
  Purchase #2 $110.75   11.381%   $123.3545   $123.35   $123.35   $123.40  
  Purchase #3 $185.63   10.209%   $204.581   $204.58   $204.60   $204.60  
  Purchase #4 $145.81   6.421%   $155.1725   $155.17   $155.15   $155.20  
  Purchase #5 $119.69   6.252%   $127.173   $127.17   $127.15   $127.20  
  Purchase #6 $63.92   10.410%   $70.5741   $70.57   $70.55   $70.60  
  Purchase #7 $131.65   6.643%   $140.3955   $140.40   $140.40   $140.40  
  7 purchase totals = $794.80       $862.5145   $862.50   $862.45   $862.70