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 $206.93   12.156%   $232.0844   $232.08   $232.10   $232.10  
  Purchase #2 $248.42   12.436%   $279.3135   $279.31   $279.30   $279.30  
  Purchase #3 $201.75   8.272%   $218.4388   $218.44   $218.45   $218.40  
  Purchase #4 $55.31   6.152%   $58.7127   $58.71   $58.70   $58.70  
  Purchase #5 $47.94   11.130%   $53.2757   $53.28   $53.30   $53.30  
  Purchase #6 $95.88   9.593%   $105.0778   $105.08   $105.10   $105.10  
  Purchase #7 $7.40   8.625%   $8.0383   $8.04   $8.05   $8.00  
  7 purchase totals = $863.63       $954.9412   $954.94   $955.00   $954.90