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 $69.49   10.327%   $76.6662   $76.67   $76.65   $76.70  
  Purchase #2 $103.44   9.123%   $112.8768   $112.88   $112.90   $112.90  
  Purchase #3 $221.82   8.620%   $240.9409   $240.94   $240.95   $240.90  
  Purchase #4 $96.40   10.503%   $106.5249   $106.52   $106.50   $106.50  
  Purchase #5 $172.57   6.445%   $183.6921   $183.69   $183.70   $183.70  
  Purchase #6 $236.77   12.765%   $266.9937   $266.99   $267.00   $267.00  
  Purchase #7 $87.59   9.587%   $95.9873   $95.99   $96.00   $96.00  
  7 purchase totals = $988.08       $1,083.6819   $1,083.68   $1,083.70   $1,083.70