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 $14.86   3.513%   $15.382   $15.38   $15.40   $15.40  
  Purchase #2 $224.46   12.567%   $252.6679   $252.67   $252.65   $252.70  
  Purchase #3 $222.95   4.158%   $232.2203   $232.22   $232.20   $232.20  
  Purchase #4 $250.80   8.313%   $271.649   $271.65   $271.65   $271.60  
  Purchase #5 $110.72   7.567%   $119.0982   $119.10   $119.10   $119.10  
  Purchase #6 $68.29   3.170%   $70.4548   $70.45   $70.45   $70.50  
  Purchase #7 $200.78   5.486%   $211.7948   $211.79   $211.80   $211.80  
  7 purchase totals = $1,092.86       $1,173.2670   $1,173.26   $1,173.25   $1,173.30