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 $106.76   10.719%   $118.2036   $118.20   $118.20   $118.20  
  Purchase #2 $44.76   4.573%   $46.8069   $46.81   $46.80   $46.80  
  Purchase #3 $239.52   6.541%   $255.187   $255.19   $255.20   $255.20  
  Purchase #4 $6.58   11.559%   $7.3406   $7.34   $7.35   $7.30  
  Purchase #5 $166.45   8.852%   $181.1842   $181.18   $181.20   $181.20  
  Purchase #6 $250.77   5.234%   $263.8953   $263.90   $263.90   $263.90  
  Purchase #7 $135.34   3.730%   $140.3882   $140.39   $140.40   $140.40  
  7 purchase totals = $950.18       $1,013.0058   $1,013.01   $1,013.05   $1,013.00