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 $86.75   8.195%   $93.8592   $93.86   $93.85   $93.90  
  Purchase #2 $33.37   4.227%   $34.7805   $34.78   $34.80   $34.80  
  Purchase #3 $181.53   6.273%   $192.9174   $192.92   $192.90   $192.90  
  Purchase #4 $101.90   6.771%   $108.7996   $108.80   $108.80   $108.80  
  Purchase #5 $115.52   10.291%   $127.4082   $127.41   $127.40   $127.40  
  Purchase #6 $211.65   9.697%   $232.1737   $232.17   $232.15   $232.20  
  Purchase #7 $54.61   11.328%   $60.7962   $60.80   $60.80   $60.80  
  7 purchase totals = $785.33       $850.7348   $850.74   $850.70   $850.80