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 $57.94   12.636%   $65.2613   $65.26   $65.25   $65.30  
  Purchase #2 $198.41   12.251%   $222.7172   $222.72   $222.70   $222.70  
  Purchase #3 $55.79   11.608%   $62.2661   $62.27   $62.25   $62.30  
  Purchase #4 $90.50   3.290%   $93.4775   $93.48   $93.50   $93.50  
  Purchase #5 $119.84   5.546%   $126.4863   $126.49   $126.50   $126.50  
  Purchase #6 $243.42   3.551%   $252.0638   $252.06   $252.05   $252.10  
  Purchase #7 $162.26   13.227%   $183.7221   $183.72   $183.70   $183.70  
  7 purchase totals = $928.16       $1,005.9943   $1,006.00   $1,005.95   $1,006.10