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 $62.85   3.403%   $64.9888   $64.99   $65.00   $65.00  
  Purchase #2 $118.86   6.827%   $126.9746   $126.97   $126.95   $127.00  
  Purchase #3 $225.27   9.107%   $245.7853   $245.79   $245.80   $245.80  
  Purchase #4 $62.32   5.541%   $65.7732   $65.77   $65.75   $65.80  
  Purchase #5 $171.43   3.604%   $177.6083   $177.61   $177.60   $177.60  
  Purchase #6 $56.32   13.451%   $63.8956   $63.90   $63.90   $63.90  
  Purchase #7 $228.98   5.422%   $241.3953   $241.40   $241.40   $241.40  
  7 purchase totals = $926.03       $986.4211   $986.43   $986.40   $986.50