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 $41.35   12.245%   $46.4133   $46.41   $46.40   $46.40  
  Purchase #2 $219.81   10.719%   $243.3714   $243.37   $243.35   $243.40  
  Purchase #3 $84.56   7.185%   $90.6356   $90.64   $90.65   $90.60  
  Purchase #4 $229.31   8.196%   $248.1042   $248.10   $248.10   $248.10  
  Purchase #5 $217.55   10.723%   $240.8779   $240.88   $240.90   $240.90  
  Purchase #6 $242.83   8.726%   $264.0193   $264.02   $264.00   $264.00  
  Purchase #7 $129.64   5.543%   $136.8259   $136.83   $136.85   $136.80  
  7 purchase totals = $1,165.05       $1,270.2476   $1,270.25   $1,270.25   $1,270.20