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 $248.89   10.151%   $274.1548   $274.15   $274.15   $274.20  
  Purchase #2 $145.39   6.379%   $154.6644   $154.66   $154.65   $154.70  
  Purchase #3 $168.55   3.780%   $174.9212   $174.92   $174.90   $174.90  
  Purchase #4 $166.70   11.871%   $186.489   $186.49   $186.50   $186.50  
  Purchase #5 $154.52   4.411%   $161.3359   $161.34   $161.35   $161.30  
  Purchase #6 $28.96   6.411%   $30.8166   $30.82   $30.80   $30.80  
  Purchase #7 $220.65   9.120%   $240.7733   $240.77   $240.75   $240.80  
  7 purchase totals = $1,133.66       $1,223.1552   $1,223.15   $1,223.10   $1,223.20