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 $152.32   6.673%   $162.4843   $162.48   $162.50   $162.50  
  Purchase #2 $123.53   9.247%   $134.9528   $134.95   $134.95   $135.00  
  Purchase #3 $172.99   7.672%   $186.2618   $186.26   $186.25   $186.30  
  Purchase #4 $170.27   10.214%   $187.6614   $187.66   $187.65   $187.70  
  Purchase #5 $221.33   8.255%   $239.6008   $239.60   $239.60   $239.60  
  Purchase #6 $43.88   10.241%   $48.3738   $48.37   $48.35   $48.40  
  Purchase #7 $94.41   7.870%   $101.8401   $101.84   $101.85   $101.80  
  7 purchase totals = $978.73       $1,061.1750   $1,061.16   $1,061.15   $1,061.30