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 $92.91   3.290%   $95.9667   $95.97   $95.95   $96.00  
  Purchase #2 $147.30   12.783%   $166.1294   $166.13   $166.15   $166.10  
  Purchase #3 $143.83   8.736%   $156.395   $156.40   $156.40   $156.40  
  Purchase #4 $122.37   5.755%   $129.4124   $129.41   $129.40   $129.40  
  Purchase #5 $71.90   7.802%   $77.5096   $77.51   $77.50   $77.50  
  Purchase #6 $49.92   5.759%   $52.7949   $52.79   $52.80   $52.80  
  Purchase #7 $148.41   4.310%   $154.8065   $154.81   $154.80   $154.80  
  7 purchase totals = $776.64       $833.0145   $833.02   $833.00   $833.00