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 $246.27   5.194%   $259.0613   $259.06   $259.05   $259.10  
  Purchase #2 $214.58   11.670%   $239.6215   $239.62   $239.60   $239.60  
  Purchase #3 $82.86   7.202%   $88.8276   $88.83   $88.85   $88.80  
  Purchase #4 $26.55   12.822%   $29.9542   $29.95   $29.95   $30.00  
  Purchase #5 $85.77   11.367%   $95.5195   $95.52   $95.50   $95.50  
  Purchase #6 $156.56   9.384%   $171.2516   $171.25   $171.25   $171.30  
  Purchase #7 $60.26   7.851%   $64.991   $64.99   $65.00   $65.00  
  7 purchase totals = $872.85       $949.2267   $949.22   $949.20   $949.30