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 $206.26   10.734%   $228.3999   $228.40   $228.40   $228.40  
  Purchase #2 $161.86   11.369%   $180.2619   $180.26   $180.25   $180.30  
  Purchase #3 $177.65   7.849%   $191.5937   $191.59   $191.60   $191.60  
  Purchase #4 $162.30   5.847%   $171.7897   $171.79   $171.80   $171.80  
  Purchase #5 $163.51   7.180%   $175.25   $175.25   $175.25   $175.30  
  Purchase #6 $137.51   12.272%   $154.3852   $154.39   $154.40   $154.40  
  Purchase #7 $140.85   7.235%   $151.0405   $151.04   $151.05   $151.00  
  7 purchase totals = $1,149.94       $1,252.7209   $1,252.72   $1,252.75   $1,252.80