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 $15.59   4.727%   $16.3269   $16.33   $16.35   $16.30  
  Purchase #2 $160.36   5.642%   $169.4075   $169.41   $169.40   $169.40  
  Purchase #3 $238.64   10.196%   $262.9717   $262.97   $262.95   $263.00  
  Purchase #4 $49.74   7.346%   $53.3939   $53.39   $53.40   $53.40  
  Purchase #5 $240.85   13.602%   $273.6104   $273.61   $273.60   $273.60  
  Purchase #6 $110.45   4.174%   $115.0602   $115.06   $115.05   $115.10  
  Purchase #7 $169.48   3.844%   $175.9948   $175.99   $176.00   $176.00  
  7 purchase totals = $985.11       $1,066.7654   $1,066.76   $1,066.75   $1,066.80