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 $247.61   11.302%   $275.5949   $275.59   $275.60   $275.60  
  Purchase #2 $232.84   4.499%   $243.3155   $243.32   $243.30   $243.30  
  Purchase #3 $19.48   11.234%   $21.6684   $21.67   $21.65   $21.70  
  Purchase #4 $150.75   10.567%   $166.6798   $166.68   $166.70   $166.70  
  Purchase #5 $241.91   6.807%   $258.3768   $258.38   $258.40   $258.40  
  Purchase #6 $48.49   6.614%   $51.6971   $51.70   $51.70   $51.70  
  Purchase #7 $186.27   3.461%   $192.7168   $192.72   $192.70   $192.70  
  7 purchase totals = $1,127.35       $1,210.0493   $1,210.06   $1,210.05   $1,210.10