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 $184.76   5.796%   $195.4687   $195.47   $195.45   $195.50  
  Purchase #2 $118.79   10.494%   $131.2558   $131.26   $131.25   $131.30  
  Purchase #3 $213.53   5.623%   $225.5368   $225.54   $225.55   $225.50  
  Purchase #4 $77.40   10.760%   $85.7282   $85.73   $85.75   $85.70  
  Purchase #5 $50.87   6.321%   $54.0855   $54.09   $54.10   $54.10  
  Purchase #6 $165.58   3.510%   $171.3919   $171.39   $171.40   $171.40  
  Purchase #7 $68.54   8.719%   $74.516   $74.52   $74.50   $74.50  
  7 purchase totals = $879.47       $937.9829   $938.00   $938.00   $938.00