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 $206.83   8.728%   $224.8821   $224.88   $224.90   $224.90  
  Purchase #2 $228.53   8.707%   $248.4281   $248.43   $248.45   $248.40  
  Purchase #3 $185.28   8.485%   $201.001   $201.00   $201.00   $201.00  
  Purchase #4 $98.29   9.256%   $107.3877   $107.39   $107.40   $107.40  
  Purchase #5 $116.25   9.413%   $127.1926   $127.19   $127.20   $127.20  
  Purchase #6 $208.52   7.516%   $224.1924   $224.19   $224.20   $224.20  
  Purchase #7 $13.35   9.434%   $14.6094   $14.61   $14.60   $14.60  
  7 purchase totals = $1,057.05       $1,147.6933   $1,147.69   $1,147.75   $1,147.70