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 $61.60   11.792%   $68.8639   $68.86   $68.85   $68.90  
  Purchase #2 $60.32   3.299%   $62.31   $62.31   $62.30   $62.30  
  Purchase #3 $105.72   11.668%   $118.0554   $118.06   $118.05   $118.10  
  Purchase #4 $97.52   10.117%   $107.3861   $107.39   $107.40   $107.40  
  Purchase #5 $14.49   7.832%   $15.6249   $15.62   $15.60   $15.60  
  Purchase #6 $244.86   5.103%   $257.3552   $257.36   $257.35   $257.40  
  Purchase #7 $127.84   11.580%   $142.6439   $142.64   $142.65   $142.60  
  7 purchase totals = $712.35       $772.2394   $772.24   $772.20   $772.30