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 $114.97   10.777%   $127.3603   $127.36   $127.35   $127.40  
  Purchase #2 $174.34   3.364%   $180.2048   $180.20   $180.20   $180.20  
  Purchase #3 $160.44   6.818%   $171.3788   $171.38   $171.40   $171.40  
  Purchase #4 $241.62   3.578%   $250.2652   $250.27   $250.25   $250.30  
  Purchase #5 $216.55   9.854%   $237.8888   $237.89   $237.90   $237.90  
  Purchase #6 $135.44   7.602%   $145.7361   $145.74   $145.75   $145.70  
  Purchase #7 $159.88   13.284%   $181.1185   $181.12   $181.10   $181.10  
  7 purchase totals = $1,203.24       $1,293.9525   $1,293.96   $1,293.95   $1,294.00