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 $235.82   12.569%   $265.4602   $265.46   $265.45   $265.50  
  Purchase #2 $170.71   10.197%   $188.1173   $188.12   $188.10   $188.10  
  Purchase #3 $26.62   11.737%   $29.7444   $29.74   $29.75   $29.70  
  Purchase #4 $76.54   13.620%   $86.9647   $86.96   $86.95   $87.00  
  Purchase #5 $250.28   13.818%   $284.8637   $284.86   $284.85   $284.90  
  Purchase #6 $38.79   12.206%   $43.5247   $43.52   $43.50   $43.50  
  Purchase #7 $130.82   11.565%   $145.9493   $145.95   $145.95   $145.90  
  7 purchase totals = $929.58       $1,044.6243   $1,044.61   $1,044.55   $1,044.60