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 $169.61   13.178%   $191.9612   $191.96   $191.95   $192.00  
  Purchase #2 $152.36   6.780%   $162.69   $162.69   $162.70   $162.70  
  Purchase #3 $164.82   7.787%   $177.6545   $177.65   $177.65   $177.70  
  Purchase #4 $225.45   5.416%   $237.6604   $237.66   $237.65   $237.70  
  Purchase #5 $127.72   13.561%   $145.0401   $145.04   $145.05   $145.00  
  Purchase #6 $172.65   12.152%   $193.6304   $193.63   $193.65   $193.60  
  Purchase #7 $162.31   6.824%   $173.386   $173.39   $173.40   $173.40  
  7 purchase totals = $1,174.92       $1,282.0226   $1,282.02   $1,282.05   $1,282.10