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 $198.42   3.827%   $206.0135   $206.01   $206.00   $206.00  
  Purchase #2 $214.43   13.704%   $243.8155   $243.82   $243.80   $243.80  
  Purchase #3 $62.74   3.577%   $64.9842   $64.98   $65.00   $65.00  
  Purchase #4 $13.89   6.704%   $14.8212   $14.82   $14.80   $14.80  
  Purchase #5 $230.66   12.418%   $259.3034   $259.30   $259.30   $259.30  
  Purchase #6 $57.58   5.364%   $60.6686   $60.67   $60.65   $60.70  
  Purchase #7 $183.93   13.332%   $208.4515   $208.45   $208.45   $208.50  
  7 purchase totals = $961.65       $1,058.0579   $1,058.05   $1,058.00   $1,058.10