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 $90.98   5.388%   $95.882   $95.88   $95.90   $95.90  
  Purchase #2 $22.93   3.159%   $23.6544   $23.65   $23.65   $23.70  
  Purchase #3 $236.79   6.422%   $251.9967   $252.00   $252.00   $252.00  
  Purchase #4 $101.33   9.228%   $110.6807   $110.68   $110.70   $110.70  
  Purchase #5 $160.50   9.803%   $176.2338   $176.23   $176.25   $176.20  
  Purchase #6 $183.99   5.322%   $193.7819   $193.78   $193.80   $193.80  
  Purchase #7 $67.87   7.480%   $72.9467   $72.95   $72.95   $72.90  
  7 purchase totals = $864.39       $925.1762   $925.17   $925.25   $925.20