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 $120.50   11.210%   $134.0081   $134.01   $134.00   $134.00  
  Purchase #2 $229.67   4.214%   $239.3483   $239.35   $239.35   $239.30  
  Purchase #3 $240.51   13.345%   $272.6061   $272.61   $272.60   $272.60  
  Purchase #4 $94.76   8.740%   $103.042   $103.04   $103.05   $103.00  
  Purchase #5 $151.80   8.366%   $164.4996   $164.50   $164.50   $164.50  
  Purchase #6 $175.74   10.695%   $194.5354   $194.54   $194.55   $194.50  
  Purchase #7 $76.99   10.473%   $85.0532   $85.05   $85.05   $85.10  
  7 purchase totals = $1,089.97       $1,193.0927   $1,193.10   $1,193.10   $1,193.00