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 $211.98   8.520%   $230.0407   $230.04   $230.05   $230.00  
  Purchase #2 $118.98   12.228%   $133.5289   $133.53   $133.55   $133.50  
  Purchase #3 $189.37   6.451%   $201.5863   $201.59   $201.60   $201.60  
  Purchase #4 $12.36   9.293%   $13.5086   $13.51   $13.50   $13.50  
  Purchase #5 $55.54   8.490%   $60.2553   $60.26   $60.25   $60.30  
  Purchase #6 $34.58   9.858%   $37.9889   $37.99   $38.00   $38.00  
  Purchase #7 $91.81   4.847%   $96.26   $96.26   $96.25   $96.30  
  7 purchase totals = $714.62       $773.1687   $773.18   $773.20   $773.20