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 $76.37   12.496%   $85.9132   $85.91   $85.90   $85.90  
  Purchase #2 $163.77   13.730%   $186.2556   $186.26   $186.25   $186.30  
  Purchase #3 $26.57   10.107%   $29.2554   $29.26   $29.25   $29.30  
  Purchase #4 $243.34   4.518%   $254.3341   $254.33   $254.35   $254.30  
  Purchase #5 $95.65   9.593%   $104.8257   $104.83   $104.85   $104.80  
  Purchase #6 $247.53   7.320%   $265.6492   $265.65   $265.65   $265.60  
  Purchase #7 $127.64   11.239%   $141.9855   $141.99   $142.00   $142.00  
  7 purchase totals = $980.87       $1,068.2187   $1,068.23   $1,068.25   $1,068.20