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 $161.84   8.315%   $175.297   $175.30   $175.30   $175.30  
  Purchase #2 $19.52   10.141%   $21.4995   $21.50   $21.50   $21.50  
  Purchase #3 $169.42   9.836%   $186.0842   $186.08   $186.10   $186.10  
  Purchase #4 $217.42   11.157%   $241.6775   $241.68   $241.70   $241.70  
  Purchase #5 $46.95   3.509%   $48.5975   $48.60   $48.60   $48.60  
  Purchase #6 $175.68   13.122%   $198.7327   $198.73   $198.75   $198.70  
  Purchase #7 $143.74   7.641%   $154.7232   $154.72   $154.70   $154.70  
  7 purchase totals = $934.57       $1,026.6116   $1,026.61   $1,026.65   $1,026.60