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 $56.61   13.169%   $64.065   $64.07   $64.05   $64.10  
  Purchase #2 $176.62   10.532%   $195.2216   $195.22   $195.20   $195.20  
  Purchase #3 $42.41   3.329%   $43.8218   $43.82   $43.80   $43.80  
  Purchase #4 $233.44   12.782%   $263.2783   $263.28   $263.30   $263.30  
  Purchase #5 $145.45   3.494%   $150.532   $150.53   $150.55   $150.50  
  Purchase #6 $223.95   5.712%   $236.742   $236.74   $236.75   $236.70  
  Purchase #7 $119.75   3.540%   $123.9892   $123.99   $124.00   $124.00  
  7 purchase totals = $998.23       $1,077.6499   $1,077.65   $1,077.65   $1,077.60