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 $106.78   10.628%   $118.1286   $118.13   $118.15   $118.10  
  Purchase #2 $95.93   11.774%   $107.2248   $107.22   $107.20   $107.20  
  Purchase #3 $179.46   13.509%   $203.7033   $203.70   $203.70   $203.70  
  Purchase #4 $97.86   6.515%   $104.2356   $104.24   $104.25   $104.20  
  Purchase #5 $32.68   8.696%   $35.5219   $35.52   $35.50   $35.50  
  Purchase #6 $114.57   11.540%   $127.7914   $127.79   $127.80   $127.80  
  Purchase #7 $168.55   13.688%   $191.6211   $191.62   $191.60   $191.60  
  7 purchase totals = $795.83       $888.2267   $888.22   $888.20   $888.10