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 $157.33   11.355%   $175.1948   $175.19   $175.20   $175.20  
  Purchase #2 $228.93   4.613%   $239.4905   $239.49   $239.50   $239.50  
  Purchase #3 $31.84   9.581%   $34.8906   $34.89   $34.90   $34.90  
  Purchase #4 $163.49   10.161%   $180.1022   $180.10   $180.10   $180.10  
  Purchase #5 $42.46   4.341%   $44.3032   $44.30   $44.30   $44.30  
  Purchase #6 $185.50   12.696%   $209.0511   $209.05   $209.05   $209.10  
  Purchase #7 $171.47   5.204%   $180.3933   $180.39   $180.40   $180.40  
  7 purchase totals = $981.02       $1,063.4257   $1,063.41   $1,063.45   $1,063.50