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 $158.92   11.137%   $176.6189   $176.62   $176.60   $176.60  
  Purchase #2 $198.71   3.478%   $205.6211   $205.62   $205.60   $205.60  
  Purchase #3 $68.30   4.824%   $71.5948   $71.59   $71.60   $71.60  
  Purchase #4 $199.60   10.587%   $220.7317   $220.73   $220.75   $220.70  
  Purchase #5 $197.33   5.567%   $208.3154   $208.32   $208.30   $208.30  
  Purchase #6 $168.57   13.406%   $191.1685   $191.17   $191.15   $191.20  
  Purchase #7 $201.79   13.316%   $228.6604   $228.66   $228.65   $228.70  
  7 purchase totals = $1,193.22       $1,302.7108   $1,302.71   $1,302.65   $1,302.70