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 $44.44   3.583%   $46.0323   $46.03   $46.05   $46.00  
  Purchase #2 $114.31   5.381%   $120.461   $120.46   $120.45   $120.50  
  Purchase #3 $61.77   10.595%   $68.3145   $68.31   $68.30   $68.30  
  Purchase #4 $174.45   4.284%   $181.9234   $181.92   $181.90   $181.90  
  Purchase #5 $37.33   10.186%   $41.1324   $41.13   $41.15   $41.10  
  Purchase #6 $126.76   13.132%   $143.4061   $143.41   $143.40   $143.40  
  Purchase #7 $14.93   5.333%   $15.7262   $15.73   $15.75   $15.70  
  7 purchase totals = $573.99       $616.9959   $616.99   $617.00   $616.90