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 $142.86   13.398%   $162.0004   $162.00   $162.00   $162.00  
  Purchase #2 $23.93   7.526%   $25.731   $25.73   $25.75   $25.70  
  Purchase #3 $239.51   12.240%   $268.826   $268.83   $268.85   $268.80  
  Purchase #4 $91.30   4.299%   $95.225   $95.23   $95.25   $95.20  
  Purchase #5 $172.98   4.808%   $181.2969   $181.30   $181.30   $181.30  
  Purchase #6 $22.61   9.223%   $24.6953   $24.70   $24.70   $24.70  
  Purchase #7 $108.81   6.572%   $115.961   $115.96   $115.95   $116.00  
  7 purchase totals = $802.00       $873.7356   $873.75   $873.80   $873.70