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 $212.27   13.342%   $240.5911   $240.59   $240.60   $240.60  
  Purchase #2 $230.99   10.332%   $254.8559   $254.86   $254.85   $254.90  
  Purchase #3 $22.77   8.313%   $24.6629   $24.66   $24.65   $24.70  
  Purchase #4 $101.93   11.601%   $113.7549   $113.75   $113.75   $113.80  
  Purchase #5 $67.67   8.476%   $73.4057   $73.41   $73.40   $73.40  
  Purchase #6 $117.56   5.371%   $123.8741   $123.87   $123.85   $123.90  
  Purchase #7 $202.90   5.443%   $213.9438   $213.94   $213.95   $213.90  
  7 purchase totals = $956.09       $1,045.0884   $1,045.08   $1,045.05   $1,045.20