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 $96.61   11.254%   $107.4825   $107.48   $107.50   $107.50  
  Purchase #2 $22.88   13.195%   $25.899   $25.90   $25.90   $25.90  
  Purchase #3 $187.89   10.208%   $207.0698   $207.07   $207.05   $207.10  
  Purchase #4 $200.64   6.556%   $213.794   $213.79   $213.80   $213.80  
  Purchase #5 $49.88   8.232%   $53.9861   $53.99   $54.00   $54.00  
  Purchase #6 $205.27   11.627%   $229.1367   $229.14   $229.15   $229.10  
  Purchase #7 $211.84   4.536%   $221.4491   $221.45   $221.45   $221.40  
  7 purchase totals = $975.01       $1,058.8172   $1,058.82   $1,058.85   $1,058.80