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 $158.25   12.628%   $178.2338   $178.23   $178.25   $178.20  
  Purchase #2 $166.41   12.290%   $186.8618   $186.86   $186.85   $186.90  
  Purchase #3 $120.77   10.122%   $132.9943   $132.99   $133.00   $133.00  
  Purchase #4 $195.57   9.755%   $214.6479   $214.65   $214.65   $214.60  
  Purchase #5 $50.87   6.157%   $54.0021   $54.00   $54.00   $54.00  
  Purchase #6 $57.61   11.623%   $64.306   $64.31   $64.30   $64.30  
  Purchase #7 $159.51   9.653%   $174.9075   $174.91   $174.90   $174.90  
  7 purchase totals = $908.99       $1,005.9534   $1,005.95   $1,005.95   $1,005.90