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 $42.84   4.366%   $44.7104   $44.71   $44.70   $44.70  
  Purchase #2 $7.74   3.641%   $8.0218   $8.02   $8.00   $8.00  
  Purchase #3 $33.64   11.611%   $37.5459   $37.55   $37.55   $37.50  
  Purchase #4 $37.25   11.590%   $41.5673   $41.57   $41.55   $41.60  
  Purchase #5 $95.84   6.239%   $101.8195   $101.82   $101.80   $101.80  
  Purchase #6 $76.49   6.771%   $81.6691   $81.67   $81.65   $81.70  
  Purchase #7 $34.37   7.632%   $36.9931   $36.99   $37.00   $37.00  
  7 purchase totals = $328.17       $352.3271   $352.33   $352.25   $352.30