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 $177.88   10.729%   $196.9647   $196.96   $196.95   $197.00  
  Purchase #2 $78.48   11.762%   $87.7108   $87.71   $87.70   $87.70  
  Purchase #3 $147.34   6.747%   $157.281   $157.28   $157.30   $157.30  
  Purchase #4 $133.74   6.866%   $142.9226   $142.92   $142.90   $142.90  
  Purchase #5 $160.95   6.491%   $171.3973   $171.40   $171.40   $171.40  
  Purchase #6 $117.68   3.510%   $121.8106   $121.81   $121.80   $121.80  
  Purchase #7 $160.49   8.319%   $173.8412   $173.84   $173.85   $173.80  
  7 purchase totals = $976.56       $1,051.9282   $1,051.92   $1,051.90   $1,051.90