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 $243.64   10.551%   $269.3465   $269.35   $269.35   $269.30  
  Purchase #2 $160.55   10.198%   $176.9229   $176.92   $176.90   $176.90  
  Purchase #3 $172.39   8.280%   $186.6639   $186.66   $186.65   $186.70  
  Purchase #4 $219.65   5.539%   $231.8164   $231.82   $231.80   $231.80  
  Purchase #5 $179.28   7.798%   $193.2603   $193.26   $193.25   $193.30  
  Purchase #6 $203.65   3.185%   $210.1363   $210.14   $210.15   $210.10  
  Purchase #7 $228.49   9.611%   $250.4502   $250.45   $250.45   $250.50  
  7 purchase totals = $1,407.65       $1,518.5965   $1,518.60   $1,518.55   $1,518.60