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 $224.70   8.149%   $243.0108   $243.01   $243.00   $243.00  
  Purchase #2 $249.30   10.167%   $274.6463   $274.65   $274.65   $274.60  
  Purchase #3 $30.30   10.481%   $33.4757   $33.48   $33.50   $33.50  
  Purchase #4 $211.29   5.332%   $222.556   $222.56   $222.55   $222.60  
  Purchase #5 $120.54   8.379%   $130.64   $130.64   $130.65   $130.60  
  Purchase #6 $178.41   9.136%   $194.7095   $194.71   $194.70   $194.70  
  Purchase #7 $211.87   13.523%   $240.5212   $240.52   $240.50   $240.50  
  7 purchase totals = $1,226.41       $1,339.5595   $1,339.57   $1,339.55   $1,339.50