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 $66.49   7.685%   $71.5998   $71.60   $71.60   $71.60  
  Purchase #2 $219.75   9.188%   $239.9406   $239.94   $239.95   $239.90  
  Purchase #3 $41.52   13.179%   $46.9919   $46.99   $47.00   $47.00  
  Purchase #4 $196.30   8.395%   $212.7794   $212.78   $212.80   $212.80  
  Purchase #5 $153.29   10.839%   $169.9051   $169.91   $169.90   $169.90  
  Purchase #6 $56.83   9.737%   $62.3635   $62.36   $62.35   $62.40  
  Purchase #7 $34.26   11.462%   $38.1869   $38.19   $38.20   $38.20  
  7 purchase totals = $768.44       $841.7672   $841.77   $841.80   $841.80